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PNW Arizona Public Service

Cover Page

Cover Page - shares3 Months Ended
Mar. 31, 2021Apr. 28, 2021
Entity Information [Line Items]
Document Type10-Q
Document Quarterly Reporttrue
Document Period End DateMar. 31,
2021
Document Transition Reportfalse
Entity File Number1-8962
Entity Registrant NamePINNACLE WEST CAPITAL CORPORATION
Entity Tax Identification Number86-0512431
Entity Incorporation, State or Country CodeAZ
Entity Address, Address Line One400 North Fifth Street, P.O. Box 53999
Entity Address, City or TownPhoenix
Entity Address, State or ProvinceAZ
Entity Address, Postal Zip Code85072-3999
City Area Code(602)
Local Phone Number250-1000
Title of 12(b) SecurityCommon Stock
Trading SymbolPNW
Security Exchange NameNYSE
Entity Current Reporting StatusYes
Entity Interactive Data CurrentYes
Entity Filer CategoryLarge Accelerated Filer
Entity Small Businessfalse
Entity Emerging Growth Companyfalse
Entity Shell Companyfalse
Entity Common Stock, Shares Outstanding112,750,962
Entity Central Index Key0000764622
Amendment Flagfalse
Current Fiscal Year End Date--12-31
Document Fiscal Year Focus2021
Document Fiscal Period FocusQ1
APS
Entity Information [Line Items]
Document Type10-Q
Document Period End DateMar. 31,
2021
Entity File Number1-4473
Entity Registrant NameARIZONA PUBLIC SERVICE COMPANY
Entity Tax Identification Number86-0011170
Entity Incorporation, State or Country CodeAZ
Entity Address, Address Line One400 North Fifth Street, P.O. Box 53999
Entity Address, City or TownPhoenix
Entity Address, State or ProvinceAZ
Entity Address, Postal Zip Code85072-3999
City Area Code(602)
Local Phone Number250-1000
Entity Current Reporting StatusYes
Entity Interactive Data CurrentYes
Entity Filer CategoryNon-accelerated Filer
Entity Small Businessfalse
Entity Emerging Growth Companyfalse
Entity Shell Companyfalse
Entity Common Stock, Shares Outstanding71,264,947
Entity Central Index Key0000007286
Amendment Flagfalse
Current Fiscal Year End Date--12-31
Document Fiscal Year Focus2021
Document Fiscal Period FocusQ1

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
OPERATING REVENUES (NOTE 2) $ 696,475 $ 661,930
OPERATING EXPENSES
Fuel and purchased power198,227 188,521
Operations and maintenance230,055 221,318
Depreciation and amortization157,820 154,079
Taxes other than income taxes59,483 56,768
Other expenses3,356 822
Total648,941 621,508
OPERATING INCOME47,534 40,422
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction9,207 7,697
Pension and other postretirement non-service credits — net27,791 13,911
Other income (Note 9)12,429 12,569
Other expense (Note 9)(3,853)(4,784)
Total45,574 29,393
INTEREST EXPENSE
Interest charges61,938 59,234
Allowance for borrowed funds used during construction(4,994)(4,076)
Total56,944 55,158
INCOME BEFORE INCOME TAXES36,164 14,657
INCOME TAXES(4,350)(20,209)
NET INCOME40,514 34,866
Less: Comprehensive income attributable to noncontrolling interests4,873 4,873
NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS $ 35,641 $ 29,993
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - BASIC (in shares)112,829 112,594
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - DILUTED (in shares)113,093 112,862
EARNINGS PER WEIGHTED-AVERAGE COMMON SHARE OUTSTANDING
Net income attributable to common shareholders - basic (in dollars per share) $ 0.32 $ 0.27
Net income attributable to common shareholders - diluted (in dollars per share) $ 0.32 $ 0.27
APS
OPERATING REVENUES (NOTE 2) $ 696,475 $ 661,930
OPERATING EXPENSES
Fuel and purchased power198,227 188,521
Operations and maintenance226,401 218,265
Depreciation and amortization157,800 154,058
Taxes other than income taxes59,472 56,758
Other expenses3,356 822
Total645,256 618,424
OPERATING INCOME51,219 43,506
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction9,207 7,697
Pension and other postretirement non-service credits — net27,837 14,262
Other income (Note 9)11,960 11,633
Other expense (Note 9)(3,350)(4,668)
Total45,654 28,924
INTEREST EXPENSE
Interest charges59,388 55,736
Allowance for borrowed funds used during construction(4,994)(4,076)
Total54,394 51,660
INCOME BEFORE INCOME TAXES42,479 20,770
INCOME TAXES2,319 (19,448)
NET INCOME40,160 40,218
Less: Comprehensive income attributable to noncontrolling interests4,873 4,873
NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS $ 35,287 $ 35,345

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
NET INCOME $ 40,514 $ 34,866
Derivative instruments:
Net unrealized gain, net of tax benefit (expense)262 292
Reclassification of net realized gain, net of tax benefit (expense)0 20
Pension and other postretirement benefits activity, net of tax expense1,022 1,205
Total other comprehensive income1,284 1,517
COMPREHENSIVE INCOME41,798 36,383
Less: Comprehensive income attributable to noncontrolling interests4,873 4,873
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS36,925 31,510
APS
NET INCOME40,160 40,218
Derivative instruments:
Net unrealized gain, net of tax benefit (expense)0 292
Reclassification of net realized gain, net of tax benefit (expense)0 20
Pension and other postretirement benefits activity, net of tax expense927 1,013
Total other comprehensive income927 1,325
COMPREHENSIVE INCOME41,087 41,543
Less: Comprehensive income attributable to noncontrolling interests4,873 4,873
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS $ 36,214 $ 36,670

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Net unrealized gain, tax benefit (expense) $ (86) $ 292
Reclassification of net realized gain, tax expense0 394
Pension and other postretirement benefits activity, tax expense336 245
APS
Net unrealized gain, tax benefit (expense)0 292
Reclassification of net realized gain, tax expense0 394
Pension and other postretirement benefits activity, tax expense $ 305 $ 237

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
CURRENT ASSETS
Cash and cash equivalents $ 17,202 $ 59,968
Customer and other receivables263,126 313,576
Accrued unbilled revenues122,034 132,197
Allowance for doubtful accounts(20,405)(19,782)
Materials and supplies (at average cost)314,702 314,745
Fossil fuel (at average cost)24,396 19,552
Income tax receivable0 6,792
Assets from risk management activities (Note 7)22,611 2,931
Deferred fuel and purchased power regulatory asset (Note 4)228,609 175,835
Other regulatory assets (Note 4)111,271 115,878
Other current assets86,238 76,627
Total current assets1,169,784 1,198,319
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)1,159,699 1,138,435
Other special use funds (Notes 11 and 12)357,506 254,509
Other assets88,487 92,922
Total investments and other assets1,605,692 1,485,866
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use20,948,591 20,837,885
Accumulated depreciation and amortization(7,189,708)(7,110,310)
Net13,758,883 13,727,575
Construction work in progress1,056,991 937,384
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)97,068 98,036
Intangible assets, net of accumulated amortization278,226 282,570
Nuclear fuel, net of accumulated amortization124,533 113,645
Total property, plant and equipment15,315,701 15,159,210
DEFERRED DEBITS
Regulatory assets (Note 4)1,135,857 1,133,987
Operating lease right-of-use assets502,959 505,064
Assets for pension and other postretirement benefits (Note 5)418,427 502,992
Other36,238 34,983
Total deferred debits2,093,481 2,177,026
TOTAL ASSETS20,184,658 20,020,421
CURRENT LIABILITIES
Accounts payable309,145 318,585
Accrued taxes213,536 159,551
Accrued interest58,709 56,962
Common dividends payable0 93,531
Short-term borrowings (Note 3)214,750 169,000
Customer deposits45,170 48,340
Liabilities from risk management activities (Note 7)3,067 7,557
Liabilities for asset retirements16,021 15,586
Operating lease liabilities74,328 74,785
Regulatory liabilities (Note 4)250,228 229,088
Other current liabilities145,589 187,448
Total current liabilities1,330,543 1,360,433
Long-term debt less current maturities (Note 3)6,465,045 6,314,266
DEFERRED CREDITS AND OTHER
Deferred income taxes2,134,471 2,135,403
Regulatory liabilities (Note 4)2,427,769 2,450,169
Liabilities for asset retirements693,383 689,497
Liabilities for pension benefits (Note 5)164,230 166,484
Liabilities from risk management activities (Note 7)6,928 11,062
Customer advances220,999 221,032
Coal mine reclamation171,227 170,097
Deferred investment tax credit190,842 191,372
Unrecognized tax benefits5,870 5,834
Operating lease liabilities360,497 361,336
Other206,174 190,643
Total deferred credits and other6,582,390 6,592,929
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 112,791,565 and 112,760,051 issued at respective dates2,687,052 2,677,482
Treasury stock at cost; 44,338 and 72,006 shares at respective dates(3,776)(6,289)
Total common stock2,683,276 2,671,193
Retained earnings3,060,752 3,025,106
Accumulated other comprehensive loss(61,512)(62,796)
Total shareholders’ equity5,682,516 5,633,503
Noncontrolling interests (Note 6)124,164 119,290
Total equity5,806,680 5,752,793
TOTAL LIABILITIES AND EQUITY20,184,658 20,020,421
APS
CURRENT ASSETS
Cash and cash equivalents14,536 57,310
Customer and other receivables262,636 312,644
Accrued unbilled revenues122,034 132,197
Allowance for doubtful accounts(20,405)(19,782)
Materials and supplies (at average cost)314,702 314,745
Fossil fuel (at average cost)24,396 19,552
Assets from risk management activities (Note 7)22,611 2,931
Deferred fuel and purchased power regulatory asset (Note 4)228,609 175,835
Other regulatory assets (Note 4)111,271 115,878
Other current assets56,987 47,593
Total current assets1,137,377 1,158,903
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)1,159,699 1,138,435
Other special use funds (Notes 11 and 12)357,506 254,509
Other assets44,829 46,010
Total investments and other assets1,562,034 1,438,954
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use20,945,129 20,834,424
Accumulated depreciation and amortization(7,186,452)(7,107,058)
Net13,758,677 13,727,366
Construction work in progress1,056,991 937,384
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)97,068 98,036
Intangible assets, net of accumulated amortization278,071 282,415
Nuclear fuel, net of accumulated amortization124,533 113,645
Total property, plant and equipment15,315,340 15,158,846
DEFERRED DEBITS
Regulatory assets (Note 4)1,135,857 1,133,987
Operating lease right-of-use assets501,395 503,475
Assets for pension and other postretirement benefits (Note 5)410,933 495,673
Other35,751 34,413
Total deferred debits2,083,936 2,167,548
TOTAL ASSETS20,098,687 19,924,251
CURRENT LIABILITIES
Accounts payable301,675 311,699
Accrued taxes211,174 148,970
Accrued interest56,454 56,322
Common dividends payable0 93,500
Short-term borrowings (Note 3)199,500 0
Customer deposits45,170 48,340
Liabilities from risk management activities (Note 7)3,067 7,557
Liabilities for asset retirements16,021 15,586
Operating lease liabilities74,235 74,695
Regulatory liabilities (Note 4)250,228 229,088
Other current liabilities152,290 190,420
Total current liabilities1,309,814 1,176,177
Long-term debt less current maturities (Note 3)5,818,520 5,817,945
DEFERRED CREDITS AND OTHER
Deferred income taxes2,150,668 2,143,673
Regulatory liabilities (Note 4)2,427,769 2,450,169
Liabilities for asset retirements693,383 689,497
Liabilities for pension benefits (Note 5)147,235 148,943
Liabilities from risk management activities (Note 7)6,928 11,062
Customer advances220,999 221,032
Coal mine reclamation171,227 170,097
Deferred investment tax credit190,842 191,372
Unrecognized tax benefits39,863 39,410
Operating lease liabilities358,840 359,653
Other176,324 160,036
Total deferred credits and other6,584,078 6,584,944
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock178,162 178,162
Additional paid-in capital2,871,696 2,871,696
Retained earnings3,252,244 3,216,955
Accumulated other comprehensive loss(39,991)(40,918)
Total shareholders’ equity6,262,111 6,225,895
Noncontrolling interests (Note 6)124,164 119,290
Total equity6,386,275 6,345,185
Total capitalization12,204,795 12,163,130
TOTAL LIABILITIES AND EQUITY $ 20,098,687 $ 19,924,251

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - sharesMar. 31, 2021Dec. 31, 2020
EQUITY
Common stock, authorized shares (in shares)150,000,000 150,000,000
Common stock, issued shares (in shares)112,791,565 112,760,051
Treasury stock at cost, shares (in shares)44,338 72,006

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income $ 40,514 $ 34,866
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization including nuclear fuel176,409 173,168
Deferred fuel and purchased power(52,210)(5,785)
Deferred fuel and purchased power amortization(564)(1,808)
Allowance for equity funds used during construction(9,207)(7,697)
Deferred income taxes(11,077)(18,086)
Deferred investment tax credit(529)(465)
Stock compensation11,337 6,282
Changes in current assets and liabilities:
Customer and other receivables50,545 25,575
Accrued unbilled revenues10,163 34,731
Materials, supplies and fossil fuel(4,801)5,445
Income tax receivable6,792 1,128
Other current assets(9,042)(20,202)
Accounts payable24,465 (5,192)
Accrued taxes53,985 49,833
Other current liabilities(46,028)(63,096)
Change in other long-term assets(36,777)81,143
Change in other long-term liabilities(1,963)(106,212)
Net cash flow provided by operating activities202,012 183,628
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures(363,775)(340,014)
Contributions in aid of construction15,296 3,152
Allowance for borrowed funds used during construction(4,994)(4,076)
Proceeds from nuclear decommissioning trust sales and other special use funds379,978 195,087
Investment in nuclear decommissioning trust and other special use funds(380,548)(195,658)
Other5,974 349
Net cash flow used for investing activities(348,069)(341,160)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of long-term debt150,000 0
Short-term borrowing and (repayments) — net49,750 (76,675)
Short-term debt borrowings under revolving credit facility0 751,690
Short-term debt repayments under revolving credit facility(4,000)(226,690)
Repayment of long-term debt0 (150,000)
Dividends paid on common stock(91,721)(86,257)
Common stock equity issuance — net of purchases(738)(1,680)
Net cash flow provided by financing activities103,291 210,388
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS(42,766)52,856
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD59,968 10,283
CASH AND CASH EQUIVALENTS AT END OF PERIOD17,202 63,139
APS
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income40,160 40,218
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization including nuclear fuel176,389 173,147
Deferred fuel and purchased power(52,210)(5,785)
Deferred fuel and purchased power amortization(564)(1,808)
Allowance for equity funds used during construction(9,207)(7,697)
Deferred income taxes(2,616)(17,782)
Deferred investment tax credit(529)(465)
Changes in current assets and liabilities:
Customer and other receivables50,103 15,045
Accrued unbilled revenues10,163 34,731
Materials, supplies and fossil fuel(4,801)5,445
Income tax receivable0 (1,411)
Other current assets(8,825)(18,164)
Accounts payable23,881 (4,038)
Accrued taxes62,204 54,243
Other current liabilities(43,917)(49,149)
Change in other long-term assets(36,626)82,178
Change in other long-term liabilities(642)(105,117)
Net cash flow provided by operating activities202,963 193,591
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures(363,775)(340,014)
Contributions in aid of construction15,296 3,152
Allowance for borrowed funds used during construction(4,994)(4,076)
Proceeds from nuclear decommissioning trust sales and other special use funds379,978 195,087
Investment in nuclear decommissioning trust and other special use funds(380,548)(195,658)
Other2,306 (900)
Net cash flow used for investing activities(351,737)(342,409)
CASH FLOWS FROM FINANCING ACTIVITIES
Short-term borrowing and (repayments) — net199,500 0
Short-term debt borrowings under revolving credit facility0 540,000
Short-term debt repayments under revolving credit facility0 (110,000)
Repayment of long-term debt0 (150,000)
Dividends paid on common stock(93,500)(88,000)
Net cash flow provided by financing activities106,000 192,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS(42,774)43,182
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD57,310 10,169
CASH AND CASH EQUIVALENTS AT END OF PERIOD $ 14,536 $ 53,351

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in ThousandsTotalCommon StockTreasury StockRetained EarningsAccumulated Other Comprehensive Income (Loss)Noncontrolling InterestsAPSAPSCommon StockAPSAdditional Paid-In CapitalAPSRetained EarningsAPSAccumulated Other Comprehensive Income (Loss)APSNoncontrolling Interests
Beginning balance (in shares) at Dec. 31, 2019112,540,126 103,546 71,264,947
Balance at beginning of period at Dec. 31, 2019 $ 5,553,188 $ 2,659,561 $ (9,427) $ 2,837,610 $ (57,096) $ 122,540 $ 5,998,803 $ 178,162 $ 2,721,696 $ 3,011,927 $ (35,522) $ 122,540
Increase (Decrease) in Shareholders' Equity
Net Income34,866 29,993 4,873 40,218 35,345 4,873
Other comprehensive income (loss)1,517 1,517 1,325 1,325
Dividends on common stock8 8
Issuance of common stock (in shares)23,484
Issuance of common stock4,826 $ 4,826
Purchase of treasury stock (in shares)[1](20,724)
Purchase of treasury stock[1](2,086) $ (2,086)
Reissuance of treasury stock for stock-based compensation and other (in shares)51,968
Reissuance of treasury stock for stock-based compensation and other4,513 $ 4,513
Other0 1 1 (2)(3)1
Ending balance (in shares) at Mar. 31, 2020112,563,610 72,302 71,264,947
Balance at end of period at Mar. 31, 2020 $ 5,596,832 $ 2,664,387 $ (7,000)2,867,610 (55,579)127,414 6,040,344 $ 178,162 2,721,696 3,047,269 (34,197)127,414
Beginning balance (in shares) at Dec. 31, 2020112,760,051 112,760,051 72,006 71,264,947
Balance at beginning of period at Dec. 31, 2020 $ 5,752,793 $ 2,677,482 $ (6,289)3,025,106 (62,796)119,290 6,345,185 $ 178,162 2,871,696 3,216,955 (40,918)119,290
Increase (Decrease) in Shareholders' Equity
Net Income40,514 35,641 4,873 40,160 35,287 4,873
Other comprehensive income (loss)1,284 1,284 927 927
Dividends on common stock5 5
Issuance of common stock (in shares)31,514
Issuance of common stock9,570 $ 9,570
Purchase of treasury stock (in shares)[1](17,437)
Purchase of treasury stock[1](1,333) $ (1,333)
Reissuance of treasury stock for stock-based compensation and other (in shares)45,105
Reissuance of treasury stock for stock-based compensation and other3,846 $ 3,846
Other $ 1 1 3 2 1
Ending balance (in shares) at Mar. 31, 2021112,791,565 112,791,565 44,338 71,264,947
Balance at end of period at Mar. 31, 2021 $ 5,806,680 $ 2,687,052 $ (3,776) $ 3,060,752 $ (61,512) $ 124,164 $ 6,386,275 $ 178,162 $ 2,871,696 $ 3,252,244 $ (39,991) $ 124,164
[1]Primarily represents shares of common stock withheld from certain stock awards for tax purposes.

Consolidation and Nature of Ope

Consolidation and Nature of Operations3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidation and Nature of OperationsConsolidation and Nature of Operations The unaudited condensed consolidated financial statements include the accounts of Pinnacle West and our subsidiaries: APS, 4C Acquisition, LLC (“4CA”), Bright Canyon Energy Corporation (“BCE”) and El Dorado Investment Company (“El Dorado”). See Note 8 for more information on 4CA matters. Intercompany accounts and transactions between the consolidated companies have been eliminated. The unaudited condensed consolidated financial statements for APS include the accounts of APS and the Palo Verde Generating Station (“Palo Verde”) sale leaseback variable interest entities (“VIEs”) (see Note 6 for further discussion). Our accounting records are maintained in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Amounts reported in our interim Condensed Consolidated Statements of Income are not necessarily indicative of amounts expected for the respective annual periods, due to the effects of seasonal temperature variations on energy consumption, timing of maintenance on electric generating units (“EGU”), and other factors. Our condensed consolidated financial statements reflect all adjustments (consisting only of normal recurring adjustments except as otherwise disclosed in the notes) that we believe are necessary for the fair presentation of our financial position, results of operations, and cash flows for the periods presented. Certain information and footnote disclosures normally included in financial statements prepared in conformity with GAAP have been condensed or omitted pursuant to such regulations, although we believe that the disclosures provided are adequate to make the interim information presented not misleading. The accompanying condensed consolidated financial statements and these notes should be read in conjunction with the audited consolidated financial statements and notes included in our 2020 Form 10-K. On June 30, 2020, the United States Federal Energy Regulatory Commission (“FERC”) issued an order granting a waiver request related to the existing Allowance for Funds Used During Construction (“AFUDC”) rate calculation beginning March 1, 2020 through February 28, 2021. On February 23, 2021, this waiver was extended until September 30, 2021. The order provides a simplified approach that companies may elect to implement in order to minimize the significant distorted effect on the AFUDC formula resulting from increased short-term debt financing during the COVID-19 pandemic. APS has adopted this simplified approach to computing the AFUDC composite rate by using a simple average of the actual historical short-term debt balances for 2019, instead of current period short-term debt balances, and has left all other aspects of the AFUDC formula composite rate calculation unchanged. This change impacts the AFUDC composite rate in both 2020 and 2021 but does not impact prior years. Furthermore, the change in the composite rate calculation does not impact our accounting treatment for these costs. The change will not have a material impact on our financial statements. See Note 1 in our 2020 Form 10-K for information on the accounting treatment for AFUDC. Supplemental Cash Flow Information The following table summarizes supplemental Pinnacle West cash flow information (dollars in thousands): Three Months Ended 2021 2020 Cash paid during the period for: Income taxes, net of refunds $ (827) $ (3,002) Interest, net of amounts capitalized 53,885 53,723 Significant non-cash investing and financing activities: Accrued capital expenditures $ 79,597 $ 100,868 Right-of-use operating lease assets obtained in exchange for operating lease liabilities 785 2,311 The following table summarizes supplemental APS cash flow information (dollars in thousands): Three Months Ended 2021 2020 Cash paid during the period for: Income taxes, net of refunds $ — $ — Interest, net of amounts capitalized 53,153 52,034 Significant non-cash investing and financing activities: Accrued capital expenditures $ 79,597 $ 100,868 Right-of-use operating lease assets obtained in exchange for operating lease liabilities 785 2,311

Revenue

Revenue3 Months Ended
Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
RevenueRevenue Sources of Revenue The following table provides detail of Pinnacle West’s consolidated revenue disaggregated by revenue sources (dollars in thousands): Three Months Ended March 31, 2021 2020 Retail Electric Revenue Residential $ 340,838 $ 325,073 Non-Residential 314,783 303,351 Wholesale Energy Sales 17,597 14,668 Transmission Services for Others 18,993 15,927 Other Sources 4,264 2,911 Total operating revenues $ 696,475 $ 661,930 Retail Electric Revenue. Pinnacle West’s retail electric revenue is generated by wholly-owned regulated subsidiary APS’s sale of electricity to our regulated customers within the authorized service territory at tariff rates approved by the ACC and based on customer usage. Revenues related to the sale of electricity are generally recognized when service is rendered or electricity is delivered to customers. The billing of electricity sales to individual customers is based on the reading of their meters. We obtain customers’ meter data on a systematic basis throughout the month, and generally bill customers within a month from when service was provided. Customers are generally required to pay for services within 15 days of when the services are billed. See “Allowance for Doubtful Accounts” discussion below for additional details regarding payment terms. Wholesale Energy Sales and Transmission Services for Others. Revenues from wholesale energy sales and transmission services for others represent energy and transmission sales to wholesale customers. These activities primarily consist of managing fuel and purchased power risks in connection with the cost of serving our retail customers’ energy requirements. We may also sell into the wholesale markets generation that is not needed for APS’s retail load. Our wholesale activities and tariff rates are regulated by FERC. In the electricity business, some contracts to purchase energy are settled by netting against other contracts to sell electricity. This is referred to as a book-out, and usually occurs in contracts that have the same terms (product type, quantities, and delivery points) and for which power does not flow. We net these book-outs, which reduces both wholesale revenues and fuel and purchased power costs. Revenue Activities Our revenues primarily consist of activities that are classified as revenues from contracts with customers. We derive our revenues from contracts with customers primarily from sales of electricity to our regulated retail customers. Revenues from contracts with customers also include wholesale and transmission activities. Our revenues from contracts with customers for the three months ended March 31, 2021 and 2020 were $682 million and $648 million, respectively. We have certain revenues that do not meet the specific accounting criteria to be classified as revenues from contracts with customers. For the three months ended March 31, 2021 and 2020, our revenues that do not qualify as revenue from contracts with customers were $14 million and $14 million, respectively. This relates primarily to certain regulatory cost recovery mechanisms that are considered alternative revenue programs. We recognize revenue associated with alternative revenue programs when specific events permitting recognition are completed. Certain amounts associated with alternative revenue programs will subsequently be billed to customers; however, we do not reclassify billed amounts into revenue from contracts with customers. See Note 4 for a discussion of our regulatory cost recovery mechanisms. Contract Assets and Liabilities from Contracts with Customers There were no material contract assets, contract liabilities, or deferred contract costs recorded on the Condensed Consolidated Balance Sheets as of March 31, 2021 or December 31, 2020. Allowance for Doubtful Accounts The allowance for doubtful accounts represents our best estimate of accounts receivable and accrued unbilled revenues that will ultimately be uncollectible due to credit loss risk. The allowance includes a write-off component that is calculated by applying an estimated write-off factor to retail electric revenues. The write-off factor used to estimate uncollectible accounts is based upon consideration of historical collections experience, the current and forecasted economic environment, changes to our collection policies, and management’s best estimate of future collections success. On March 13, 2020, due to the COVID-19 pandemic we voluntarily suspended disconnections of customers for nonpayment. The suspension of customer disconnections was extended from March 13, 2020 through December 31, 2020. Our disconnection policies are also impacted by the Summer Disconnection Moratorium. The suspension of disconnection of customers for nonpayment ended on January 1, 2021 and certain customers with past due balances were placed on eight-month payment arrangements. These circumstances and the on-going COVID-19 pandemic have impacted our allowance for doubtful accounts, including our write-off factor. We continue to monitor the impacts of COVID-19, our disconnection policies, payment arrangements, among other considerations impacting our estimated write-off factor and allowance for doubtful accounts. See Note 4 for additional details. The following table provides a rollforward of Pinnacle West’s allowance for doubtful accounts (dollars in thousands): March 31, 2021 December 31, 2020 Allowance for doubtful accounts, balance at beginning of period $ 19,782 $ 8,171 Bad debt expense 4,151 20,633 Actual write-offs (3,528) (9,022) Allowance for doubtful accounts, balance at end of period $ 20,405 $ 19,782

Long-Term Debt and Liquidity Ma

Long-Term Debt and Liquidity Matters3 Months Ended
Mar. 31, 2021
Debt Disclosure [Abstract]
Long-Term Debt and Liquidity MattersLong-Term Debt and Liquidity Matters Pinnacle West and APS maintain committed revolving credit facilities in order to enhance liquidity and provide credit support for their commercial paper programs, to refinance indebtedness, and for other general corporate purposes. Pinnacle West On May 5, 2020, Pinnacle West refinanced its 364-day $50 million term loan agreement with a new 364-day $31 million term loan agreement that would have matured May 4, 2021. Borrowings under the agreement bore interest at Eurodollar Rate plus 1.40% per annum. At March 31, 2021, Pinnacle West had $15 million in outstanding borrowings under the current agreement, all of which was repaid on April 27, 2021. On December 23, 2020, Pinnacle West entered into a $150 million term loan facility that matures June 2022. The proceeds were received on January 4, 2021 and used for general corporate purposes. We recognized the term loan facility as long-term debt upon settlement on January 4, 2021. At March 31, 2021, Pinnacle West had a $200 million revolving credit facility that matures in July 2023. Pinnacle West has the option to increase the amount of the facility up to a maximum of $300 million upon the satisfaction of certain conditions and with the consent of the lenders. Interest rates are based on Pinnacle West’s senior unsecured debt credit ratings. The facility is available to support Pinnacle West’s $200 million commercial paper program, for bank borrowings or for issuances of letters of credits. At March 31, 2021, Pinnacle West had no outstanding borrowings under its credit facility, no letters of credit outstanding and $0.3 million of outstanding commercial paper borrowings. APS At March 31, 2021, APS had two revolving credit facilities totaling $1 billion, including a $500 million credit facility that matures in June 2022 and a $500 million facility that matures in July 2023. APS may increase the amount of each facility up to a maximum of $700 million, for a total of $1.4 billion, upon the satisfaction of certain conditions and with the consent of the lenders. Interest rates are based on APS’s senior unsecured debt credit ratings. These facilities are available to support APS’s $750 million commercial paper program, for bank borrowings or for issuances of letters of credit. At March 31, 2021, APS had no outstanding borrowings under its revolving credit facilities, no letters of credit outstanding, and $199.5 million of outstanding commercial paper borrowings. On December 17, 2020, the ACC issued a financing order in which, subject to specified parameters and procedures, it approved APS’s short-term debt authorization equal to the sum of (i) 7% of APS’s capitalization, and (ii) $500 million (which is required to be used for costs relating to purchases of natural gas and power) and a long-term debt authorization of $7.5 billion. See “Financial Assurances” in Note 8 for a discussion of other outstanding letters of credit. Debt Fair Value Our long-term debt fair value estimates are classified within Level 2 of the fair value hierarchy. The following table presents the estimated fair value of our long-term debt, including current maturities (dollars in thousands): As of March 31, 2021 As of December 31, 2020 Carrying Fair Value Carrying Fair Value Pinnacle West $ 646,525 $ 653,395 $ 496,321 $ 509,050 APS 5,818,520 6,436,224 5,817,945 7,103,791 Total $ 6,465,045 $ 7,089,619 $ 6,314,266 $ 7,612,841

Regulatory Matters

Regulatory Matters3 Months Ended
Mar. 31, 2021
Regulated Operations [Abstract]
Regulatory MattersRegulatory Matters COVID-19 Pandemic Due to the COVID-19 pandemic, APS voluntarily suspended disconnections of customers for nonpayment and waived late payment fees beginning March 13, 2020 until December 31, 2020. The suspension of disconnection of customers for nonpayment ended on January 1, 2021 and customers were automatically placed on eight-month payment arrangements if they had past due balances at the end of the disconnection period of $75 or greater. APS will continue to waive late payment fees until October 15, 2021. APS has experienced and is continuing to experience an increase in bad debt expense associated with the COVID-19 pandemic, the Summer Disconnection Moratorium (defined below) and the related write-offs of customer delinquent accounts. Due to COVID-19, APS also delayed the reset of the Environmental Improvement Surcharge (“EIS”) adjustor and suspended the discontinuation of TEAM Phase II to the first billing cycle in May 2020 rather than April 2020. In February 2021, APS delayed the annual reset of the PSA. Rather than the increase being effective February 2021, the PSA reset will be implemented with 50% of the increase effective April 2021 and the remaining 50% increase effective November 2021 (see below for discussion of EIS, TEAM Phase II and PSA). On April 17, 2020, APS filed an application with the ACC requesting a COVID-19 emergency relief package to provide additional assistance to its customers. On May 5, 2020, the ACC approved APS returning $36 million that had been collected through the Demand Side Management (“DSM”) Adjustor Charge, but not allocated for current DSM programs, directly to customers through a bill credit in June 2020. APS has refunded approximately $43 million to customers. The additional $7 million over the approved amount of $36 million was the result of the kWh credit being based on historic consumption, which was different than actual consumption in the refund period. This difference was recorded to the DSM balancing account and will be addressed in subsequent DSM filings (see below for discussion of the DSM Adjustor Charge). In 2020, APS spent more than $15 million to assist customers and local non-profits and community organizations to help with the impact of the COVID-19 pandemic, with $12.4 million of these dollars directly committed to bill assistance programs (the “COVID Customer Support Fund”). The COVID Customer Support Fund was comprised of a series of voluntary commitments of funds that are not recoverable through rates throughout 2020 of approximately $8.8 million. An additional $3.6 million in bill credits for limited income customers was ordered by the ACC in December 2020 of which 50%, up to a maximum of $2.5 million, was committed to be funds that are not recoverable through rates with the remaining being deferred for potential future recovery in rates. Included in the COVID Customer Support Fund were programs that assisted customers that had a delinquency of two or more months with a one-time credit of $100, an expanded credit of $300 for limited income customers, programs to assist extra small and small non-residential customers with a one-time credit of $1,000, and other targeted programs allocated to assist with other COVID-19 needs in support of utility bill assistance. The December 2020 ACC order further assisted delinquent limited income customers with an additional bill credit of up to $250 or their delinquent balance, whichever was less. APS has distributed all funds for all COVID Customer Support Fund programs combined. Beyond the COVID Customer Support Fund, APS has also provided $2.7 million to assist local non-profits and community organizations working to mitigate the impacts of the COVID-19 pandemic. 2019 Retail Rate Case Filing with the Arizona Corporation Commission In accordance with the requirements of the 2019 rate review order described below, APS filed an application with the ACC on October 31, 2019 seeking an increase in annual retail base rates of $69 million. This amount includes recovery of the deferral and rate base effects of the Four Corners selective catalytic reduction (“SCR”) project that is currently the subject of a separate proceeding (see “SCR Cost Recovery” below). It also reflects a net credit to base rates of approximately $115 million primarily due to the prospective inclusion of rate refunds currently provided through the Tax Expense Adjustment Mechanism (“TEAM”). The proposed total annual revenue increase in APS’s application is $184 million. The average annual customer bill impact of APS’s request is an increase of 5.6% (the average annual bill impact for a typical APS residential customer is 5.4%). The principal provisions of APS’s application were: • a test year comprised of twelve months ended June 30, 2019, adjusted as described below; • an original cost rate base of $8.87 billion, which approximates the ACC-jurisdictional portion of the book value of utility assets, net of accumulated depreciation and other credits; • the following proposed capital structure and costs of capital: Capital Structure Cost of Capital Long-term debt 45.3 % 4.10 % Common stock equity 54.7 % 10.15 % Weighted-average cost of capital 7.41 % • a 1% return on the increment of fair value rate base above APS’s original cost rate base, as provided for by Arizona law; • a rate of $0.030168 per kWh for the portion of APS’s retail base rates attributable to fuel and purchased power costs (“Base Fuel Rate”); • authorization to defer until APS’s next general rate case the increase or decrease in its Arizona property taxes attributable to tax rate changes after the date the rate application is adjudicated; • a number of proposed rate and program changes for residential customers, including: ▪ a super off-peak period during the winter months for APS’s time-of-use with demand rates; ▪ additional $1.25 million in funding for APS’s limited-income crisis bill program; and ▪ a flat bill/subscription rate pilot program; • proposed rate design changes for commercial customers, including an experimental program designed to provide access to market pricing for up to 200 MW of medium and large commercial customers; • recovery of the deferral and rate base effects of the construction and operating costs of the Ocotillo modernization project (see discussion below of the 2017 Settlement Agreement); and • continued recovery of the remaining investment and other costs related to the retirement and closure of the Navajo Generating Station (the “Navajo Plant”) (see “Navajo Plant” below). On October 2, 2020, the ACC Staff, the Residential Utility Consumer Office (“RUCO”) and other intervenors filed their initial written testimony with the ACC in this rate case. The ACC Staff recommends, among other things, a (i) $89.7 million revenue increase, (ii) average annual customer bill increase of 2.7%, (iii) return on equity of 9.4%, (iv) a 0.3% or, as an alternative, a 0% return on the increment of fair value rate base greater than original cost , (v) recovery of the deferral and rate base effects of the construction and operating costs of the Four Corners SCR project and (vi) recovery of the rate base effects of the construction and ongoing consideration of the deferral of the Ocotillo modernization project. RUCO recommends, among other things, a (i) $20.8 million revenue decrease, (ii) average annual customer bill decrease of 0.63%, (iii) return on equity of 8.74%, (iv) a 0% return on the increment of fair value rate base, (v) nonrecovery of the deferral and rate base effects of the construction and operating costs of the Four Corners SCR project pending further consideration, and (vi) recovery of the deferral and rate base effects of the construction and operating costs of the Ocotillo modernization project. The filed ACC Staff and intervenor testimony include additional recommendations, some of which materially differ from APS’s filed application. On November 6, 2020, APS filed its rebuttal testimony and the principal provisions which differ from its initial application include, among other things, a (i) $169 million revenue increase, (ii) average annual customer bill increase of 5.14%, (iii) return on equity of 10%, (iv) return on the increment of fair value rate base of 0.8%, (v) new cost recovery adjustor mechanism, the Advanced Energy Mechanism (“AEM”), to enable more timely recovery of clean investments as APS pursues its clean energy commitment, (vi) recognition that securitization is a potentially useful financing tool to recover the remaining book value of retiring assets and effectuate a transition to a cleaner energy future that APS intends to pursue, provided legislative hurdles are addressed, and (vii) a Coal Community Transition (“CCT”) plan related to the closure or future closure of coal-fired generation facilities, of which $25 million would be funds that are not recoverable through rates with a proposal that the remainder be funded by customers over 10 years. The CCT plan includes the following proposed components: (i) $100 million that will be paid over 10 years to the Navajo Nation for a sustainable transition to a post-coal economy, which would be funded by customers, (ii) $1.25 million that will be paid over five years to the Navajo Nation to fund an economic development organization, which would be funds not recoverable through rates, (iii) $10 million to facilitate electrification projects within the Navajo Nation, which would be funded equally by funds not recoverable through rates and by customers, (iv) $2.5 million per year in transmission revenue sharing to be paid to the Navajo Nation beginning after the closure of the Four Corners Power Plant through 2038, which would be funds not recoverable through rates, (v) $12 million that will be paid over five years to the Navajo County Communities surrounding Cholla Power Plant, which would primarily be funded by customers, and (vi) $3.7 million that will be paid over five years to the Hopi Tribe related to APS’s ownership interests in the Navajo Generating Station, which would primarily be funded by customers. The commitment of funds that would not be recoverable through rates of $25 million were recognized in our December 31, 2020 financials. On December 4, 2020, the ACC Staff and intervenors filed surrebuttal testimony. The ACC Staff reduced its recommended rate increase to $59.8 million, or an average annual customer bill increase of 1.82%. In RUCO’s surrebuttal, the recommended revenue decrease changed to $50.1 million, or an average annual customer bill decrease of 1.52%. The hearing concluded on March 3, 2021 and the post-hearing briefing schedule concluded on April 30, 2021. In May 2021, the ACC will be discussing whether to re-open the evidentiary record in APS’s pending rate case to take additional evidence on topics raised by certain ACC Commissioners, including adjustor cost recovery mechanisms. APS believes that the rate case record is sufficient, and adjustors provide substantial benefits to customers by supporting critical programs and reflecting changes in utility costs that can be promptly passed along to customers. Pending this decision, the next steps in this rate case are that the Administrative Law Judge will issue a Recommended Order and Opinion and then the ACC will review and consider the matter, which is anticipated to be in the third quarter of 2021. Unfavorable ACC Staff and intervenor positions and recommendations, including modifications or elimination of APS's adjustor cost recovery mechanisms could have a material impact on APS’s financial statements if ultimately adopted by the ACC. APS cannot predict the outcome or timing of this proceeding. 2016 Retail Rate Case Filing with the Arizona Corporation Commission On June 1, 2016, APS filed an application with the ACC for an annual increase in retail base rates. On March 27, 2017, a majority of the stakeholders in the general retail rate case, including the ACC Staff, RUCO, limited income advocates and private rooftop solar organizations signed a settlement agreement (the “2017 Settlement Agreement”) and filed it with the ACC. The 2017 Settlement Agreement provides for a net retail base rate increase of $94.6 million, excluding the transfer of adjustor balances, consisting of: (1) a non-fuel, non-depreciation, base rate increase of $87.2 million per year; (2) a base rate decrease of $53.6 million attributable to reduced fuel and purchased power costs; and (3) a base rate increase of $61.0 million due to changes in depreciation schedules. The average annual customer bill impact under the 2017 Settlement Agreement was calculated as an increase of 3.28% (the average annual bill impact for a typical APS residential customer was calculated as an increase of 4.54%). Other key provisions of the agreement include the following: • an authorized return on common equity of 10.0%; • a capital structure comprised of 44.2% debt and 55.8% common equity; • a cost deferral order for potential future recovery in APS’s next general retail rate case for the construction and operating costs APS incurs for its Ocotillo modernization project; • a cost deferral and procedure to allow APS to request rate adjustments prior to its next general retail rate case related to its share of the construction costs associated with installing SCR equipment at the Four Corners Power Plant (“Four Corners”); • a deferral for future recovery (or credit to customers) of the Arizona property tax expense above or below a specified test year level caused by changes to the applicable Arizona property tax rate; • an expansion of the Power Supply Adjustor (“PSA”) to include certain environmental chemical costs and third-party energy storage costs; • a new AZ Sun II program (now known as “APS Solar Communities”) for utility-owned solar distributed generation with the purpose of expanding access to rooftop solar for low and moderate income Arizonans, recoverable through the Arizona Renewable Energy Standard and Tariff (“RES”), to be no less than $10 million per year in capital costs, and not more than $15 million per year in capital costs; • an increase to the per kWh cap for the environmental improvement surcharge from $0.00016 to $0.00050 and the addition of a balancing account; • rate design changes, including: ▪ a change in the on-peak time of use period from noon-7 p.m. to 3 p.m.-8 p.m. Monday through Friday, excluding holidays; ▪ non-grandfathered distributed generation (“DG”) customers would be required to select a rate option that has time of use rates and either a new grid access charge or demand component; ▪ a Resource Comparison Proxy (“RCP”) for exported energy of 12.9 cents per kWh in year one; and • an agreement by APS not to pursue any new self-build generation (with certain exceptions) having an in-service date prior to January 1, 2022 (extended to December 31, 2027 for combined-cycle generating units), unless expressly authorized by the ACC. Through a separate agreement, APS, industry representatives, and solar advocates committed to stand by the 2017 Settlement Agreement and refrain from seeking to undermine it through ballot initiatives, legislation or advocacy at the ACC. On August 15, 2017, the ACC approved (by a vote of 4-1) the 2017 Settlement Agreement without material modifications. On August 18, 2017, the ACC issued a final written Opinion and Order reflecting its decision in APS’s general retail rate case (the “2017 Rate Case Decision”), which is subject to requests for rehearing and potential appeal. The new rates went into effect on August 19, 2017. On January 3, 2018, an APS customer filed a petition with the ACC that was determined by the ACC Staff to be a complaint filed pursuant to Arizona Revised Statute §40-246 (the “Complaint”). The Complaint was later amended alleging that the rates and charges in the 2017 Rate Case Decision are not just and reasonable. The ACC held a hearing on this matter, and the Administrative Law Judge issued a Recommended Opinion and Order recommending that the Complaint be dismissed. On July 3, 2019, the Administrative Law Judge issued an amendment to the Recommended Opinion and Order that incorporated the requirements of the rate review of the 2017 Rate Case Decision (see below discussion regarding the rate review). On July 10, 2019, the ACC adopted the Administrative Law Judge’s amended Recommended Opinion and Order along with several ACC Commissioner amendments and an amendment incorporating the results of the rate review and resolved the Complaint. See “Rate Plan Comparison Tool and Investigation” below for information regarding a review and investigation pertaining to the rate plan comparison tool offered to APS customers and other related issues. ACC Review of APS 2017 Rate Case Decision On December 24, 2018, certain ACC Commissioners filed a letter stating that because the ACC had received a substantial number of complaints that the rate increase authorized by the 2017 Rate Case Decision was much more than anticipated, they believe there is a possibility that APS is earning more than was authorized by the 2017 Rate Case Decision. Accordingly, the ACC Commissioners requested the ACC Staff to perform a rate review of APS using calendar year 2018 as a test year. The ACC Commissioners also asked the ACC Staff to evaluate APS’s efforts to educate its customers regarding the new rates approved in the 2017 Rate Case Decision. On June 4, 2019, the ACC Staff filed a proposed order regarding the rate review of the 2017 Rate Case Decision. On June 11, 2019, the ACC Commissioners approved the proposed ACC Staff order with amendments. The key provisions of the amended order include the following: • APS must file a rate case no later than October 31, 2019, using a June 30, 2019 test year; • until the conclusion of the rate case being filed no later than October 31, 2019, APS must provide information on customer bills that shows how much a customer would pay on their most economical rate given their actual usage during each month; • APS customers can switch rate plans during an open enrollment period of six months; • APS must identify customers whose bills have increased by more than 9% and that are not on the most economical rate and provide such customers with targeted education materials and an opportunity to switch rate plans; • APS must provide grandfathered net metering customers on legacy demand rates an opportunity to switch to another legacy rate to enable such customers to fully benefit from legacy net metering rates; • APS must fund and implement a supplemental customer education and outreach program to be developed with and administered by ACC Staff and a third-party consultant; and • APS must fund and organize, along with the third-party consultant, a stakeholder group to suggest better ways to communicate the impact of changes to adjustor cost recovery mechanisms (see below for discussion on cost recovery mechanisms), including more effective ways to educate customers on rate plans and to reduce energy usage. APS filed its rate case on October 31, 2019 (see “2019 Retail Rate Case Filing with the Arizona Corporation Commission” above for more information). APS does not believe that the implementation of the other key provisions of the amended order regarding the rate review will have a material impact on its financial position, results of operations or cash flows. On May 19, 2020, the ACC Staff filed a third-party consultant’s report which evaluated the effectiveness of APS’s customer outreach and education program related to the 2017 Rate Case Decision. On May 29, 2020, the Chairman of the ACC filed a letter with the ACC in response to this report and is alleging that APS is out of compliance with the 2017 Rate Case Decision and is over-earning. The Chairman proposed that the current rates should be classified as interim rates and customers held harmless if APS’s activities have caused the rates set in the 2017 Rate Case Decision to not be just and reasonable. Also, on May 29, 2020, a second commissioner filed a letter with the ACC agreeing with the Chairman’s assertions and further asserting that the 2017 Rate Case Decision should be re-opened. On June 18, 2020, at an ACC Open Meeting, the matters raised in these letters were discussed. The ACC did not vote to move forward with any adjustments to APS’s current rates. On November 4, 2020, the ACC voted to administratively close this docket. Cost Recovery Mechanisms APS has received regulatory decisions that allow for more timely recovery of certain costs outside of a general retail rate case through the following recovery mechanisms. Renewable Energy Standard . In 2006, the ACC approved the RES. Under the RES, electric utilities that are regulated by the ACC must supply an increasing percentage of their retail electric energy sales from eligible renewable resources, including solar, wind, biomass, biogas and geothermal technologies. In order to achieve these requirements, the ACC allows APS to include a RES surcharge as part of customer bills to recover the approved amounts for use on renewable energy projects. Each year APS is required to file a five-year implementation plan with the ACC and seek approval for funding the upcoming year’s RES budget. In 2015, the ACC revised the RES rules to allow the ACC to consider all available information, including the number of rooftop solar arrays in a utility’s service territory, to determine compliance with the RES. On November 20, 2017, APS filed an updated 2018 RES budget to include budget adjustments for APS Solar Communities (formerly known as AZ Sun II), which was approved as part of the 2017 Rate Case Decision. APS Solar Communities is a 3-year program authorizing APS to spend $10 million to $15 million in capital costs each year to install utility-owned DG systems for low to moderate income residential homes, non-profit entities, Title I schools and rural government facilities. The 2017 Rate Case Decision provided that all operations and maintenance expenses, property taxes, marketing and advertising expenses, and the capital carrying costs for this program will be recovered through the RES. On June 29, 2018, APS filed its 2019 RES Implementation Plan and proposed a budget of approximately $89.9 million. APS’s budget request supports existing approved projects and commitments and requests a permanent waiver of the residential distributed energy requirement for 2019 contained in the RES rules. On October 29, 2019, the ACC approved the 2019 RES Implementation Plan including a waiver of the residential distributed energy requirements for the 2019 implementation year. On July 1, 2019, APS filed its 2020 RES Implementation Plan and proposed a budget of approximately $86.3 million. APS’s budget request supports existing approved projects and commitments and requests a permanent waiver of the residential distributed energy requirement for 2020 contained in the RES rules. On September 23, 2020, the ACC approved the 2020 RES Implementation Plan including a waiver of the residential distributed energy requirements for the 2020 implementation year. In addition, the ACC approved the implementation of a new pilot program that incentivizes Arizona households to install at-home battery systems. Recovery of the costs associated with the pilot will be addressed in the 2021 Demand Side Management Implementation Plan (“DSM Plan”). On July 1, 2020, APS filed its 2021 RES Implementation Plan and proposed a budget of approximately $84.7 million. APS’s budget request supports existing approved projects and commitments and requests a permanent waiver of the residential distributed energy requirement for 2021 contained in the RES rules. In the 2021 RES Implementation Plan, APS requested $4.5 million to meet revenue requirements associated with the APS Solar Communities program to complete installations delayed as a result of the COVID-19 pandemic in 2020. The ACC has not yet ruled on the 2021 RES Implementation Plan. On July 30, 2020, ACC Staff issued final draft rules which, if approved, would require APS to meet certain clean energy standards and technology procurement mandates, obtain approval for its action plan included in its IRP, and seek cost recovery in a rate process. APS cannot predict the outcome of this matter. See “Energy Modernization Plan” below for more information. Demand Side Management Adjustor Charge . The ACC Electric Energy Efficiency Standards require APS to submit a DSM Plan annually for review by and approval of the ACC. Verified energy savings from APS’s resource savings projects can be counted toward compliance with the Electric Energy Efficiency Standards; however, APS is not allowed to count savings from systems savings projects toward determination of the achievement of performance incentives, nor may APS include savings from these system savings projects in the calculation of its Lost Fixed Cost Recovery (“LFCR”) mechanism (see below for discussion of the LFCR). On September 1, 2017, APS filed its 2018 DSM Plan, which proposed modifications to the demand side management portfolio to better meet system and customer needs by focusing on peak demand reductions, storage, load shifting and demand response programs in addition to traditional energy savings measures. The 2018 DSM Plan sought a requested budget of $52.6 million and requested a waiver of the Electric Energy Efficiency Standard for 2018. On November 14, 2017, APS filed an amended 2018 DSM Plan, which revised the allocations between budget items to address customer participation levels but kept the overall budget at $52.6 million. On December 31, 2018, APS filed its 2019 DSM Plan, which requested a budget of $34.1 million and focused on DSM strategies to better meet system and customer needs, such as peak demand reduction, load shifting, storage and electrification strategies. On December 31, 2019, APS filed its 2020 DSM Plan, which requested a budget of $51.9 million and continued APS’s focus on DSM strategies such as peak demand reduction, load shifting, storage and electrification strategies. The 2020 DSM Plan addressed all components of the pending 2018 and 2019 DSM plans, which enabled the ACC to review the 2020 DSM Plan only. On May 15, 2020, APS filed an amended 2020 DSM Plan to provide assistance to customers experiencing economic impacts of the COVID-19 pandemic. The amended 2020 DSM Plan requested the same budget amount of $51.9 million. On September 23, 2020, the ACC approved the amended 2020 DSM Plan. On April 17, 2020, APS filed an application with the ACC requesting a COVID-19 emergency relief package to provide additional assistance to its customers. On May 5, 2020, the ACC approved APS returning $36 million that had been collected through the DSM Adjustor Charge, but not allocated for current DSM programs, directly to customers through a bill credit in June 2020. APS has refunded approximately $43 million to customers. The additional $7 million over the approved amount was the result of the kWh credit being based on historic consumption which was different than actual consumption in the refund period. This difference was recorded to the DSM balancing account and will be addressed in subsequent DSM filings. See “COVID-19 Pandemic” above for more information. On December 31, 2020, APS filed its 2021 DSM Plan, which requested a budget of $63.7 million and continued APS’s focus on DSM strategies, such as peak demand reduction, load shifting, storage and electrification strategies, as well as enhanced assistance to customers impacted economically by COVID-19. On April 6, 2021, APS filed an amended 2021 DSM Plan that proposed an additional performance incentive for customers participating in the residential energy storage pilot approved in the 2020 RES Implementation Plan. The ACC has not yet ruled on the amended APS 2021 DSM Plan. On April 20, 2021, APS filed a request to extend the June 1, 2021 deadline to file its 2022 DSM Plan until 120 days after the ACC has taken action on APS's amended 2021 DSM Plan. The ACC has not ruled on this request. Power Supply Adjustor Mechanism and Balance. The PSA provides for the adjustment of retail rates to reflect variations primarily in retail fuel and purchased power costs. The following table shows the changes in the deferred fuel and purchased power regulatory asset for 2021 and 2020 (dollars in thousands): Three Months Ended 2021 2020 Beginning balance $ 175,835 $ 70,137 Deferred fuel and purchased power costs — current period 52,210 5,785 Amounts refunded to customers 564 1,808 Ending balance $ 228,609 $ 77,730 The PSA rate for the PSA year beginning February 1, 2019 was $0.001658 per kWh, as compared to the $0.004555 per kWh for the prior year. This rate was comprised of a forward component of $0.000536 per kWh and a historical component of $0.001122 per kWh. This represented a $0.002897 per kWh decrease compared to 2018. These rates went into effect as filed on February 1, 2019. On November 27, 2019, APS filed its PSA rate for the PSA year beginning February 1, 2020. That rate was $(0.000456) per kWh and consisted of a forward component of $(0.002086) per kWh and a historical component of $0.001630 per kWh. The 2020 PSA rate is a $0.002115 per kWh decrease compared to the 2019 PSA year. These rates went into effect as filed on February 1, 2020. On November 30, 2020, APS filed its PSA rate for the PSA year beginning February 1, 2021. That rate was $0.003544 per kWh and consisted of a forward component of $0.003434 per kWh and a historical component of $0.000110 per kWh. The 2021 PSA rate is a $0.004 per kWh increase, compared to the 2020 PSA year. These rates were to be effective on February 1, 2021 but APS delayed the effectiveness of these rates until the first billing cycle of April 2021 due to concerns of the impact on customers during COVID-19. In March 2021, the ACC voted to implement the 2021 PSA, with 50% of the rate increase effective in April 2021 and the remaining 50% of the increase effective in November 2021. The PSA rate implemented was $0.001544 per kWh and consisted of a forward component of $(0.004444) per kWh and a historical component of $0.005988 per kWh. As part of this approval, the ACC ordered ACC Staff to conduct a fuel and purchased power procurement audit to better understand the factors that contributed to the increase. On March 15, 2019, APS filed an application with the ACC requesting approval to recover the costs related to two energy storage power purchase tolling agreements through the PSA. On December 29, 2020, the ACC Staff filed its report and recommended the storage costs be included in the PSA once the systems are in-service. On January 12, 2021, the ACC approved this application. Environmental Improvement Surcharge. The EIS permits APS to recover the capital carrying costs (rate of return, depreciation and taxes) plus incremental operations and maintenance expenses associated with environmental improvements made outside of a test year to comply with environmental standards set by federal, state, tribal, or local laws and regulations. A filing is made on or before February 1 for qualified environmental improvements made during the prior calendar year, and the new charge becomes effective April 1 unless suspended by the ACC. There is an overall cap of $0.0005 per kWh (approximately $13 million to $14 million per year). APS’s February 1, 2021 application requested an increase in the charge to $10.3 million, or $1.5 million over the prior-period charge and it became effective with the first billing cycle in April 2021. Transmission Rates, Transmission Cost Adjustor (“TCA”) and Other Transmission Matters . In July 2008, FERC approved a modification to APS’s Open Access Transmission Tariff to allow APS to move from fixed rates to a formula rate-setting methodology in order to more accurately reflect and recover the costs that APS incurs in providing transmission services. A large portion of the rate represents charges for transmission services to serve APS’s retail customers (“Retail Transmission Charges”). In order to recover the Retail Transmission Charges, APS was previously required to file an application with, and obtain approval from, the ACC to reflect changes in Retail Transmission Charges through the TCA. Under the terms of the settlement agreement entered into in 2012 regarding APS’s rate case (“2012 Settlement Agreement”), however, an adjustment to rates to recover the Retail Transmission Charges will be made annually each June 1 and will go into effect automatically unless suspended by the ACC. The formula rate is updated each year effective June 1 on t

Retirement Plans and Other Post

Retirement Plans and Other Postretirement Benefits3 Months Ended
Mar. 31, 2021
Retirement Benefits [Abstract]
Retirement Plans and Other Postretirement BenefitsRetirement Plans and Other Postretirement Benefits Pinnacle West sponsors a qualified defined benefit and account balance pension plan, a non-qualified supplemental excess benefit retirement plan, and other postretirement benefit plans for the employees of Pinnacle West and our subsidiaries. The other postretirement benefit plans include a group life and medical plan and a post-65 retiree health reimbursement arrangement (“HRA”). Pinnacle West uses a December 31 measurement date each year for its pension and other postretirement benefit plans. The market-related value of our plan assets is their fair value at the measurement date. Under the HRA, included in the other postretirement benefit plan, the Company provides a subsidy to retirees to defray the cost of a Medicare supplemental policy. In prior years, we had been assuming a 4.75% escalation of these benefits; however, actual escalation has been significantly less than this assumption. Accordingly, during 2020 and for future periods, the escalation assumption was reduced to 2.00%. This escalation factor assumption change, among other factors, resulted in an increase in the over-funded status of the other postretirement benefit plan as of December 31, 2020. As a result, on January 4, 2021, we initiated the transfer of approximately $106 million of assets from the other postretirement benefit plan into the Active Union Employee Medical Account. The Active Union Employee Medical Account is an existing trust account that holds assets restricted for paying active union employee medical costs (see Note 12). The transfer of other postretirement benefit plan assets into the Active Union Employee Medical Account permits access to approximately $106 million of assets for the sole purpose of paying active union employee medical benefits. This transfer of assets into the Active Union Employee Medical Account is consistent with the terms of a similar 2018 transaction. The following table provides details of the plans’ net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction or billed to electric plant participants) (dollars in thousands): Pension Benefits Other Benefits Three Months Ended Three Months Ended 2021 2020 2021 2020 Service cost — benefits earned during the period $ 15,679 $ 14,257 $ 4,557 $ 5,717 Non-service costs (credits): Interest cost on benefit obligation 24,669 29,761 4,162 6,512 Expected return on plan assets (50,608) (46,806) (10,361) (10,019) Amortization of: Prior service credit — — (9,427) (9,394) Net actuarial loss (gain) 3,985 9,011 (2,405) — Net periodic benefit cost/(benefit) $ (6,275) $ 6,223 $ (13,474) $ (7,184) Portion of cost/(benefit) charged to expense $ (8,011) $ 1,342 $ (9,528) $ (5,456) Contributions We have not made voluntary contributions to our pension plan year-to-date in 2021. The minimum required contributions for the pension plan are zero for the next three years. We expect to make voluntary contributions up to $100 million in 2021 and zero in 2022 and 2023. We do not expect to make any contributions over this period to our other postretirement benefit plans.

Palo Verde Sale Leaseback Varia

Palo Verde Sale Leaseback Variable Interest Entities3 Months Ended
Mar. 31, 2021
Variable Interest Entities [Abstract]
Palo Verde Sale Leaseback Variable Interest EntitiesPalo Verde Sale Leaseback Variable Interest Entities In 1986, APS entered into agreements with three separate VIE lessor trust entities in order to sell and lease back interests in Palo Verde Unit 2 and related common facilities. Prior to April 1, 2021, the lease terms allowed APS the right to retain the assets through 2023 under one lease and 2033 under the other two leases. On April 1, 2021, APS executed an amended lease agreement with one of the VIE lessor trust entities relating to the lease agreement with the term ending in 2023. The amendment extends the lease term for this lease through 2033 and changes the lease payment. As a result of this amendment, APS will now retain the assets through 2033 under all three lease agreements. APS will be required to make payments relating to the three leases in total of approximately $21 million annually for the period 2021 through 2033. At the end of the lease period, APS will have the option to purchase the leased assets at their fair market value, extend the leases for up to two years, or return the assets to the lessors. The leases’ terms give APS the ability to utilize the assets for a significant portion of the assets’ economic life, and therefore provide APS with the power to direct activities of the VIEs that most significantly impact the VIEs’ economic performance. Predominantly due to the lease terms, APS has been deemed the primary beneficiary of these VIEs and therefore consolidates the VIEs. As a result of consolidation, we eliminate lease accounting and instead recognize depreciation expense, resulting in an increase in net income for the three months ended March 31, 2021 and 2020 of $5 million, entirely attributable to the noncontrolling interests. Income attributable to Pinnacle West shareholders is not impacted by the consolidation. Our Condensed Consolidated Balance Sheets at March 31, 2021 and December 31, 2020 include the following amounts relating to the VIEs (dollars in thousands): March 31, 2021 December 31, 2020 Palo Verde sale leaseback property, plant and equipment, net of accumulated depreciation $ 97,068 $ 98,036 Equity — Noncontrolling interests 124,164 119,290 Assets of the VIEs are restricted and may only be used for payment to the noncontrolling interest holders. These assets are reported on our condensed consolidated financial statements. APS is exposed to losses relating to these VIEs upon the occurrence of certain events that APS does not consider to be reasonably likely to occur. Under certain circumstances (for example, the Nuclear Regulatory Commission (“NRC”) issuing specified violation orders with respect to Palo Verde or the occurrence of specified nuclear events), APS would be required to make specified payments to the VIEs’ noncontrolling equity participants and take title to the leased Unit 2 interests, which, if appropriate, may be required to be written down in value. If such an event were to occur during the lease periods, APS may be required to pay the noncontrolling equity participants approximately $307 million beginning in 2021, and up to $501 million over the lease terms. For regulatory ratemaking purposes, the agreements continue to be treated as operating leases and, as a result, we have recorded a regulatory asset relating to the arrangements.

Derivative Accounting

Derivative Accounting3 Months Ended
Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative AccountingDerivative Accounting Derivative financial instruments are used to manage exposure to commodity price and transportation costs of electricity, natural gas, emissions allowances, and in interest rates. Risks associated with market volatility are managed by utilizing various physical and financial derivative instruments, including futures, forwards, options and swaps. As part of our overall risk management program, we may use derivative instruments to hedge purchases and sales of electricity and natural gas. Derivative instruments that meet certain hedge accounting criteria may be designated as cash flow hedges and are used to limit our exposure to cash flow variability on forecasted transactions. The changes in market value of such instruments have a high correlation to price changes in the hedged transactions. Derivative instruments are also entered into for economic hedging purposes. While economic hedges may mitigate exposure to fluctuations in commodity prices, these instruments have not been designated as accounting hedges. Contracts that have the same terms (quantities, delivery points and delivery periods) and for which power does not flow are netted, which reduces both revenues and fuel and purchased power costs in our Condensed Consolidated Statements of Income, but does not impact our financial condition, net income or cash flows. Our derivative instruments, excluding those qualifying for a scope exception, are recorded on the balance sheets as an asset or liability and are measured at fair value. See Note 11 for a discussion of fair value measurements. Derivative instruments may qualify for the normal purchases and normal sales scope exception if they require physical delivery and the quantities represent those transacted in the normal course of business. Derivative instruments qualifying for the normal purchases and sales scope exception are accounted for under the accrual method of accounting and excluded from our derivative instrument discussion and disclosures below. For its regulated operations, APS defers for future rate treatment 100% of the unrealized gains and losses on derivatives pursuant to the PSA mechanism that would otherwise be recognized in income. Realized gains and losses on derivatives are deferred in accordance with the PSA to the extent the amounts are above or below the Base Fuel Rate (see Note 4). Gains and losses from derivatives in the following tables represent the amounts reflected in income before the effect of PSA deferrals. The following table shows the outstanding gross notional volume of derivatives, which represent both purchases and sales (does not reflect net position): Quantity Commodity Unit of Measure March 31, 2021 December 31, 2020 Power GWh 368 368 Gas Billion cubic feet 211 205 Gains and Losses from Derivative Instruments The following table provides information about APS’s gains and losses from derivative instruments in designated cash flow accounting hedging relationships (dollars in thousands): Financial Statement Location Three Months Ended Commodity Contracts 2021 2020 Loss Reclassified from Accumulated OCI into Income (Effective Portion Realized) (a) Fuel and purchased power (b) $ — $ (414) (a) During the three months ended March 31, 2021 and 2020, we had no gains or losses reclassified from accumulated OCI to earnings related to discontinued cash flow hedges . (b) Amounts are before the effect of PSA deferrals. During the next twelve months, we estimate that no amounts will be reclassified from accumulated OCI into income. For APS, the delivery period for all derivative instruments in designated cash flow accounting hedging relationships have lapsed. The following table provides information about gains and losses from derivative instruments not designated as accounting hedging instruments (dollars in thousands): Financial Statement Location Three Months Ended Commodity Contracts 2021 2020 Net Gain (Loss) Recognized in Income Fuel and purchased power (a) $ 26,859 $ (30,078) (a) Amounts are before the effect of PSA deferrals. Derivative Instruments in the Condensed Consolidated Balance Sheets Our derivative transactions are typically executed under standardized or customized agreements, which include collateral requirements and, in the event of a default, would allow for the netting of positive and negative exposures associated with a single counterparty. Agreements that allow for the offsetting of positive and negative exposures associated with a single counterparty are considered master netting arrangements. Transactions with counterparties that have master netting arrangements are offset and reported net on the Condensed Consolidated Balance Sheets. Transactions that do not allow for offsetting of positive and negative positions are reported gross on the Condensed Consolidated Balance Sheets. We do not offset a counterparty’s current derivative contracts with the counterparty’s non-current derivative contracts, although our master netting arrangements would allow current and non-current positions to be offset in the event of a default. These types of transactions may include non-derivative instruments, derivatives qualifying for scope exceptions, trade receivables and trade payables arising from settled positions, and other forms of non-cash collateral (such as letters of credit). These types of transactions are excluded from the offsetting tables presented below. The following tables provide information about the fair value of our risk management activities reported on a gross basis and the impacts of offsetting. These amounts relate to commodity contracts and are located in the assets and liabilities from risk management activities and other assets lines of our Condensed Consolidated Balance Sheets. As of March 31, 2021: Gross Recognized Derivatives (a) Amounts Net Recognized Derivatives Other (c) Amount Reported on Balance Sheet Current assets $ 25,703 $ (3,092) $ 22,611 $ — $ 22,611 Investments and other assets 3,990 (790) 3,200 — 3,200 Total assets 29,693 (3,882) 25,811 — 25,811 Current liabilities (4,874) 3,092 (1,782) (1,285) (3,067) Deferred credits and other (7,718) 790 (6,928) — (6,928) Total liabilities (12,592) 3,882 (8,710) (1,285) (9,995) Total $ 17,101 $ — $ 17,101 $ (1,285) $ 15,816 (a) All of our gross recognized derivative instruments were subject to master netting arrangements. (b) No cash collateral has been provided to counterparties, or received from counterparties, that is subject to offsetting. (c) Represents cash collateral that is not subject to offsetting. Amounts relate to non-derivative instruments, derivatives qualifying for scope exceptions or collateral posted in excess of the recognized derivative instrument. Includes cash collateral received from counterparties of $1,285. As of December 31, 2020: Gross Recognized Derivatives (a) Amounts Net Recognized Derivatives Other (c) Amount Current assets $ 5,870 $ (2,939) $ 2,931 $ — $ 2,931 Investments and other assets 3,150 (1,332) 1,818 — 1,818 Total assets 9,020 (4,271) 4,749 — 4,749 Current liabilities (9,211) 2,939 (6,272) (1,285) (7,557) Deferred credits and other (12,394) 1,332 (11,062) — (11,062) Total liabilities (21,605) 4,271 (17,334) (1,285) (18,619) Total $ (12,585) $ — $ (12,585) $ (1,285) $ (13,870) (a) All of our gross recognized derivative instruments were subject to master netting arrangements. (b) No cash collateral has been provided to counterparties, or received from counterparties, that is subject to offsetting. (c) Represents cash collateral and cash margin that is not subject to offsetting. Amounts relate to non-derivative instruments, derivatives qualifying for scope exceptions, or collateral and margin posted in excess of the recognized derivative instrument. Includes cash collateral received from counterparties of $1,285. Credit Risk and Credit Related Contingent Features We are exposed to losses in the event of nonperformance or nonpayment by counterparties and have risk management contracts with many counterparties. As of March 31, 2021, we have one counterparty for which our exposure represents approximately 59% of Pinnacle West’s $26 million of risk management assets. This exposure relates to a master agreement with a counterparty that is rated as investment grade. Our risk management process assesses and monitors the financial exposure of all counterparties. Despite the fact that the great majority of our trading counterparties’ debt is rated as investment grade by the credit rating agencies, there is still a possibility that one or more of these companies could default, resulting in a material impact on consolidated earnings for a given period. Counterparties in the portfolio consist principally of financial institutions, major energy companies, municipalities and local distribution companies. We maintain credit policies that we believe minimize overall credit risk to within acceptable limits. Determination of the credit quality of our counterparties is based upon a number of factors, including credit ratings and our evaluation of their financial condition. To manage credit risk, we employ collateral requirements and standardized agreements that allow for the netting of positive and negative exposures associated with a single counterparty. Valuation adjustments are established representing our estimated credit losses on our overall exposure to counterparties. Certain of our derivative instrument contracts contain credit-risk-related contingent features including, among other things, investment grade credit rating provisions, credit-related cross-default provisions, and adequate assurance provisions. Adequate assurance provisions allow a counterparty with reasonable grounds for uncertainty to demand additional collateral based on subjective events and/or conditions. For those derivative instruments in a net liability position, with investment grade credit contingencies, the counterparties could demand additional collateral if our debt credit rating were to fall below investment grade (below BBB- for Standard & Poor’s or Fitch or Baa3 for Moody’s). The following table provides information about our derivative instruments that have credit-risk-related contingent features (dollars in thousands): March 31, 2021 Aggregate fair value of derivative instruments in a net liability position $ 11,520 Cash collateral posted — Additional cash collateral in the event credit-risk-related contingent features were fully triggered (a) 6,674 (a) This amount is after counterparty netting and includes those contracts which qualify for scope exceptions, which are excluded from the derivative details above. We also have energy-related non-derivative instrument contracts with investment grade credit-related contingent features, which could also require us to post additional collateral of approximately $86 million if our debt credit ratings were to fall below investment grade.

Commitments and Contingencies

Commitments and Contingencies3 Months Ended
Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and ContingenciesCommitments and Contingencies Palo Verde Generating Station Spent Nuclear Fuel and Waste Disposal On December 19, 2012, APS, acting on behalf of itself and the participant owners of Palo Verde, filed a second breach of contract lawsuit against the United States Department of Energy (“DOE”) in the United States Court of Federal Claims (“Court of Federal Claims”). The lawsuit sought to recover damages incurred due to DOE’s breach of the Contract for Disposal of Spent Nuclear Fuel and/or High Level Radioactive Waste (“Standard Contract”) for failing to accept Palo Verde’s spent nuclear fuel and high level waste from January 1, 2007 through June 30, 2011, as it was required to do pursuant to the terms of the Standard Contract and the Nuclear Waste Policy Act. On August 18, 2014, APS and DOE entered into a settlement agreement, stipulating to a dismissal of the lawsuit and payment by DOE to the Palo Verde owners for certain specified costs incurred by Palo Verde during the period January 1, 2007 through June 30, 2011. In addition, the settlement agreement, as amended, provides APS with a method for submitting claims and getting recovery for costs incurred through December 31, 2022. APS has submitted six claims pursuant to the terms of the August 18, 2014 settlement agreement, for six separate time periods during July 1, 2011 through June 30, 2019. The DOE has approved and paid $99.7 million for these claims (APS’s share is $29.0 million). The amounts recovered were primarily recorded as adjustments to a regulatory liability and had no impact on reported net income. In accordance with the 2017 Rate Case Decision, this regulatory liability is being refunded to customers (see Note 4). On November 2, 2020, APS filed its seventh claim pursuant to the terms of the August 18, 2014 settlement agreement in the amount of $12.2 million (APS’s share is $3.6 million). On March 15, 2021, the DOE approved a payment of $12.1 million (APS’s share is $3.5 million) and on April 16, 2021, APS received this payment. Nuclear Insurance Public liability for incidents at nuclear power plants is governed by the Price-Anderson Nuclear Industries Indemnity Act (“Price-Anderson Act”), which limits the liability of nuclear reactor owners to the amount of insurance available from both commercial sources and an industry-wide retrospective payment plan. In accordance with the Price-Anderson Act, the Palo Verde participants are insured against public liability for a nuclear incident of up to approximately $13.7 billion per occurrence. Palo Verde maintains the maximum available nuclear liability insurance in the amount of $450 million, which is provided by American Nuclear Insurers (“ANI”). The remaining balance of approximately $13.2 billion of liability coverage is provided through a mandatory industry-wide retrospective premium program. If losses at any nuclear power plant covered by the program exceed the accumulated funds, APS could be responsible for retrospective premiums. The maximum retrospective premium per reactor under the program for each nuclear liability incident is approximately $137.6 million, subject to a maximum annual premium of approximately $20.5 million per incident. Based on APS’s ownership interest in the three Palo Verde units, APS’s maximum retrospective premium per incident for all three units is approximately $120.1 million, with a maximum annual retrospective premium of approximately $17.9 million. The Palo Verde participants maintain insurance for property damage to, and decontamination of, property at Palo Verde in the aggregate amount of $2.8 billion. APS has also secured accidental outage insurance for a sudden and unforeseen accidental outage of any of the three units. The property damage, decontamination, and accidental outage insurance are provided by Nuclear Electric Insurance Limited (“NEIL”). APS is subject to retrospective premium adjustments under all NEIL policies if NEIL’s losses in any policy year exceed accumulated funds. The maximum amount APS could incur under the current NEIL policies totals approximately $22.4 million for each retrospective premium assessment declared by NEIL’s Board of Directors due to losses. In addition, NEIL policies contain rating triggers that would result in APS providing approximately $63.3 million of collateral assurance within 20 business days of a rating downgrade to non-investment grade. The insurance coverage discussed in this and the previous paragraph is subject to certain policy conditions, sublimits and exclusions. Contractual Obligations As of March 31, 2021, our fuel and purchased power commitments have increased from the information provided in our 2020 Form 10-K. The increase is primarily due to new purchased power and energy storage commitments of approximately $550 million. The majority of the changes relate to 2026 and thereafter. Other than the item described above, there have been no material changes, as of March 31, 2021, outside the normal course of business in contractual obligations from the information provided in our 2020 Form 10-K. See Note 3 for discussion regarding changes in our short-term and long-term debt obligations. Superfund-Related Matters The Comprehensive Environmental Response Compensation and Liability Act (“Superfund” or “CERCLA”) establishes liability for the cleanup of hazardous substances found contaminating the soil, water or air. Those who released, generated, transported to or disposed of hazardous substances at a contaminated site are among the parties who are potentially responsible (“PRPs”). PRPs may be strictly, and often are jointly and severally, liable for clean-up. On September 3, 2003, EPA advised APS that EPA considers APS to be a PRP in the Motorola 52 nd Street Superfund Site, Operable Unit 3 (“OU3”) in Phoenix, Arizona. APS has facilities that are within this Superfund site. APS and Pinnacle West have agreed with EPA to perform certain investigative activities of the APS facilities within OU3. In addition, on September 23, 2009, APS agreed with EPA and one other PRP to voluntarily assist with the funding and management of the site-wide groundwater remedial investigation and feasibility study (“RI/FS”). Based upon discussions between the OU3 working group parties and EPA, along with the results of recent technical analyses prepared by the OU3 working group to supplement the RI/FS for OU3, APS anticipates finalizing the RI/FS during the second quarter of 2021. We estimate that our costs related to this investigation and study will be approximately $3 million. We anticipate incurring additional expenditures in the future, but because the overall investigation is not complete and ultimate remediation requirements are not yet finalized, at the present time expenditures related to this matter cannot be reasonably estimated. On August 6, 2013, the Roosevelt Irrigation District (“RID”) filed a lawsuit in Arizona District Court against APS and 24 other defendants, alleging that RID’s groundwater wells were contaminated by the release of hazardous substances from facilities owned or operated by the defendants. The lawsuit also alleges that, under Superfund laws, the defendants are jointly and severally liable to RID. The allegations against APS arise out of APS’s current and former ownership of facilities in and around OU3. As part of a state governmental investigation into groundwater contamination in this area, on January 25, 2015, the Arizona Department of Environmental Quality (“ADEQ”) sent a letter to APS seeking information concerning the degree to which, if any, APS’s current and former ownership of these facilities may have contributed to groundwater contamination in this area. APS responded to ADEQ on May 4, 2015. On December 16, 2016, two RID environmental and engineering contractors filed an ancillary lawsuit for recovery of costs against APS and the other defendants in the RID litigation. That same day, another RID service provider filed an additional ancillary CERCLA lawsuit against certain of the defendants in the main RID litigation, but excluded APS and certain other parties as named defendants. Because the ancillary lawsuits concern past costs allegedly incurred by these RID vendors, which were ruled unrecoverable directly by RID in November of 2016, the additional lawsuits do not increase APS’s exposure or risk related to these matters. On April 5, 2018, RID and the defendants in that particular litigation executed a settlement agreement, fully resolving RID’s CERCLA claims concerning both past and future cost recovery. APS’s share of this settlement was immaterial. In addition, the two environmental and engineering vendors voluntarily dismissed their lawsuit against APS and the other named defendants without prejudice. An order to this effect was entered on April 17, 2018. With this disposition of the case, the vendors may file their lawsuit again in the future. On August 16, 2019, Maricopa County, one of the three direct defendants in the service provider lawsuit, filed a third-party complaint seeking contribution for its liability, if any, from APS and 28 other third-party defendants. We are unable to predict the outcome of these matters; however, we do not expect the outcome to have a material impact on our financial position, results of operations or cash flows. Arizona Attorney General Matter APS received civil investigative demands from the Attorney General seeking information pertaining to the rate plan comparison tool offered to APS customers and other related issues including implementation of rates from the 2017 Settlement Agreement and its Customer Education and Outreach Plan associated with the 2017 Settlement Agreement. APS fully cooperated with the Attorney General’s Office in this matter. On February 22, 2021 APS entered into a consent agreement with the Attorney General as a way to settle the matter. The settlement results in APS paying $24.75 million, $24 million of which is being returned to customers as restitution. Environmental Matters APS is subject to numerous environmental laws and regulations affecting many aspects of its present and future operations, including air emissions of both conventional pollutants and greenhouse gases, water quality, wastewater discharges, solid waste, hazardous waste, and coal combustion residuals (“CCRs”). These laws and regulations can change from time to time, imposing new obligations on APS resulting in increased capital, operating, and other costs. Associated capital expenditures or operating costs could be material. APS intends to seek recovery of any such environmental compliance costs through our rates but cannot predict whether it will obtain such recovery. The following proposed and final rules involve material compliance costs to APS. Regional Haze Rules. APS has received the final rulemaking imposing pollution control requirements on Four Corners. EPA required the plant to install pollution control equipment that constitutes best available retrofit technology (“BART”) to lessen the impacts of emissions on visibility surrounding the plant. In addition, EPA issued a final rule for Regional Haze compliance at Cholla that does not involve the installation of new pollution controls and that will replace an earlier BART determination for this facility. See below for details of the Cholla BART approval. Four Corners. Based on EPA’s final standards, APS’s 63% share of the cost of required controls for Four Corners Units 4 and 5 was approximately $400 million, which has been incurred. In addition, APS and El Paso Electric Company (“El Paso”) entered into an asset purchase agreement providing for the purchase by APS, or an affiliate of APS, of El Paso’s 7% interest in Four Corners Units 4 and 5. 4CA purchased the El Paso interest on July 6, 2016. Navajo Transitional Energy Company, LLC (“NTEC”) purchased the interest from 4CA on July 3, 2018. See “Four Corners — 4CA Matter” below for a discussion of the NTEC purchase. The cost of the pollution controls related to the 7% interest is approximately $45 million, which was assumed by NTEC through its purchase of the 7% interest. Cholla . In early 2017, EPA approved a final rule containing a revision to Arizona’s State Implementation Plan (“SIP”) for Cholla that implemented BART requirements for this facility, which did not require the installation of any new pollution control capital improvements. In conjunction with the closure of Cholla Unit 2 in 2015, APS has committed to ceasing coal combustion within Units 1 and 3 by April 2025. PacifiCorp retired Cholla Unit 4 at the end of 2020. (See “Cholla” in Note 4 for information regarding future plans for Cholla and details related to the resulting regulatory asset). Coal Combustion Waste . On December 19, 2014, EPA issued its final regulations governing the handling and disposal of CCR, such as fly ash and bottom ash. The rule regulates CCR as a non-hazardous waste under Subtitle D of the Resource Conservation and Recovery Act (“RCRA”) and establishes national minimum criteria for existing and new CCR landfills and surface impoundments and all lateral expansions. These criteria include standards governing location restrictions, design and operating criteria, groundwater monitoring and corrective action, closure requirements and post closure care, and recordkeeping, notification, and internet posting requirements. The rule generally requires any existing unlined CCR surface impoundment to stop receiving CCR and either retrofit or close, and further requires the closure of any CCR landfill or surface impoundment that cannot meet the applicable performance criteria for location restrictions or structural integrity. Such closure requirements are deemed “forced closure” or “closure for cause” of unlined surface impoundments and are the subject of recent regulatory and judicial activities described below. Since these regulations were finalized, EPA has taken steps to substantially modify the federal rules governing CCR disposal. While certain changes have been prompted by utility industry petitions, others have resulted from judicial review, court-approved settlements with environmental groups, and statutory changes to RCRA. The following lists the pending regulatory changes that, if finalized, could have a material impact as to how APS manages CCR at its coal-fired power plants: • Following the passage of the Water Infrastructure Improvements for the Nation Act in 2016, EPA possesses authority to either authorize states to develop their own permit programs for CCR management or issue federal permits governing CCR disposal both in states without their own permit programs and on tribal lands. Although ADEQ has taken steps to develop a CCR permitting program, it is not clear when that program will be put into effect. On December 19, 2019, EPA proposed its own set of regulations governing the issuance of CCR management permits. • On March 1, 2018, as a result of a settlement with certain environmental groups, EPA proposed adding boron to the list of constituents that trigger corrective action requirements to remediate groundwater impacted by CCR disposal activities. Apart from a subsequent proposal issued on August 14, 2019 to add a specific, health-based groundwater protection standard for boron, EPA has yet to take action on this proposal. • Based on an August 21, 2018 D.C. Circuit decision, which vacated and remanded those provisions of the EPA CCR regulations that allow for the operation of unlined CCR surface impoundments, EPA recently proposed corresponding changes to federal CCR regulations. On July 29, 2020, EPA took final action on new regulations establishing revised deadlines for initiating the closure of unlined CCR surface impoundments; such disposal units were closed as of April 11, 2021. • On November 4, 2019, EPA also proposed to change the manner by which facilities that have committed to cease burning coal in the near-term may qualify for alternative closure. Such qualification would allow CCR disposal units at these plants to continue operating, even though they would otherwise be subject to forced closure under the federal CCR regulations. EPA’s July 29, 2020 final regulation adopted this proposal and now requires explicit EPA approval for facilities to utilize an alternative closure deadline. With respect to the Cholla facility, APS’s application for alternative closure (which would allow the continued disposal of CCR within the facility’s existing unlined CCR surface impoundments until the required date for ceasing coal-fired boiler operations in April 2025) was submitted to EPA on November 30, 2020 and is currently pending. This application will be subject to public comment and, potentially, judicial review. We cannot at this time predict the outcome of these regulatory proceedings or when the EPA will take final action on those matters that are still pending. Depending on the eventual outcome, the costs associated with APS’s management of CCR could materially increase, which could affect APS’s financial position, results of operations, or cash flows. APS currently disposes of CCR in ash ponds and dry storage areas at Cholla and Four Corners. APS estimates that its share of incremental costs to comply with the CCR rule for Four Corners is approximately $27 million and its share of incremental costs to comply with the CCR rule for Cholla is approximately $16 million. The Navajo Plant disposed of CCR only in a dry landfill storage area. To comply with the CCR rule for the Navajo Plant, APS’s share of incremental costs was approximately $1 million, which has been incurred. Additionally, the CCR rule requires ongoing, phased groundwater monitoring. As of October 2018, APS has completed the statistical analyses for its CCR disposal units that triggered assessment monitoring. APS determined that several of its CCR disposal units at Cholla and Four Corners will need to undergo corrective action. In addition, under the current regulations, all such disposal units must have ceased operating and initiated closure by October 31, 2020. APS initiated an assessment of corrective measures on January 14, 2019 and expects such assessment will continue through mid- to late-2021. As part of this assessment, APS continues to gather additional groundwater data and perform remedial evaluations as to the CCR disposal units at Cholla and Four Corners undergoing corrective action. In addition, APS will solicit input from the public, host public hearings, and select remedies as part of this process. Based on the work performed to date, APS currently estimates that its share of corrective action and monitoring costs at Four Corners will likely range from $10 million to $15 million, which would be incurred over 30 years. The analysis needed to perform a similar cost estimate for Cholla remains ongoing at this time. As APS continues to implement the CCR rule’s corrective action assessment process, the current cost estimates may change. Given uncertainties that may exist until we have fully completed the corrective action assessment process, we cannot predict any ultimate impacts to the Company; however, at this time we do not believe the cost estimates for Cholla and any potential change to the cost estimate for Four Corners would have a material impact on our financial position, results of operations or cash flows. Clean Power Plan/Affordable Clean Energy Regulations . On June 19, 2019, EPA took final action on its proposals to repeal EPA’s 2015 Clean Power Plan (“CPP”) and replace those regulations with a new rule, the Affordable Clean Energy (“ACE”) regulations. EPA originally finalized the CPP on August 3, 2015, and such rules would have had far broader impact on the electric power sector than the ACE regulations. The ACE regulations had been stayed pending judicial review and on January 19, 2021, the U.S. Court of Appeals for the D.C. Circuit vacated the ACE regulations and remanded them back to EPA to develop new existing power plant carbon regulations consistent with the court’s ruling. That ruling endorsed an expansive view of the federal Clean Air Act consistent with EPA’s 2015 CPP. While the Biden administration has expressed an intent to regulate carbon emissions in this sector more aggressively under the Clean Air Act, we cannot at this time predict the outcome of pending EPA rulemaking proceedings in response to the court’s recent ACE decision. Other environmental rules that could involve material compliance costs include those related to effluent limitations, the ozone national ambient air quality standard and other rules or matters involving the Clean Air Act, Clean Water Act, Endangered Species Act, RCRA, Superfund, the Navajo Nation, and water supplies for our power plants. The financial impact of complying with current and future environmental rules could jeopardize the economic viability of our coal plants or the willingness or ability of power plant participants to fund any required equipment upgrades or continue their participation in these plants. The economics of continuing to own certain resources, particularly our coal plants, may deteriorate, warranting early retirement of those plants, which may result in asset impairments. APS would seek recovery in rates for the book value of any remaining investments in the plants as well as other costs related to early retirement, but cannot predict whether it would obtain such recovery. Four Corners National Pollutant Discharge Elimination System (“NPDES”) Permit On July 16, 2018, several environmental groups filed a petition for review before the EPA Environmental Appeals Board (“EAB”) concerning the NPDES wastewater discharge permit for Four Corners, which was reissued on June 12, 2018. The environmental groups allege that the permit was reissued in contravention of several requirements under the Clean Water Act and did not contain required provisions concerning EPA’s 2015 revised effluent limitation guidelines for steam-electric EGUs, 2014 existing-source regulations governing cooling-water intake structures, and effluent limits for surface seepage and subsurface discharges from coal-ash disposal facilities. To address certain of these issues through a reconsidered permit, EPA took action on December 19, 2018 to withdraw the NPDES permit reissued in June 2018. Withdrawal of the permit moots the EAB appeal, and EPA filed a motion to dismiss on that basis. The EAB thereafter dismissed the environmental group appeal on February 12, 2019. EPA then issued a revised final NPDES permit for Four Corners on September 30, 2019. Based upon a November 1, 2019 filing by several environmental groups, the EAB again took up review of the Four Corners NPDES Permit. Oral argument on this appeal was held on September 3, 2020 and the EAB denied the environmental group petition on September 30, 2020. On January 22, 2021, the environmental groups filed a petition for review of the EAB’s decision with the U.S. Court of Appeals for the Ninth Circuit. We cannot predict the outcome of these appeal proceedings and, if such appeal is successful, whether that outcome will have a material impact on our financial position, results of operations, or cash flows. Four Corners — 4CA Matter On July 6, 2016, 4CA purchased El Paso’s 7% interest in Four Corners. NTEC purchased this 7% interest on July 3, 2018 from 4CA. NTEC purchased the 7% interest at 4CA’s book value, approximately $70 million, and is paying 4CA the purchase price over a period of four years pursuant to a secured interest-bearing promissory note. The note is secured by a portion of APS’s payments to be owed to NTEC under the 2016 Coal Supply Agreement. As of March 31, 2021, the note has a remaining balance of $23 million. NTEC continues to make payments in accordance with the terms of the note. Due to its short-remaining term, among other factors, there are no expected credit losses associated with the note. In connection with the sale, Pinnacle West guaranteed certain obligations that NTEC will have to the other owners of Four Corners, such as NTEC’s 7% share of capital expenditures and operating and maintenance expenses. Pinnacle West’s guarantee is secured by a portion of APS’s payments to be owed to NTEC under the 2016 Coal Supply Agreement. The 2016 Coal Supply Agreement contained alternate pricing terms for the 7% interest in the event NTEC did not purchase the interest. Until the time that NTEC purchased the 7% interest, the alternate pricing provisions were applicable to 4CA as the holder of the 7% interest. These terms included a formula under which NTEC must make certain payments to 4CA for reimbursement of operations and maintenance costs and a specified rate of return, offset by revenue generated by 4CA’s power sales. The amount under this formula for calendar year 2018 (up to the date that NTEC purchased the 7% interest) was approximately $10 million, which was due to 4CA on December 31, 2019. Such payment was satisfied in January 2020 by NTEC directing to 4CA a prepayment from APS of future coal payment obligations of which the prepayment has been fully utilized as of June 2020. Financial Assurances In the normal course of business, we obtain standby letters of credit and surety bonds from financial institutions and other third parties. These instruments guarantee our own future performance and provide third parties with financial and performance assurance in the event we do not perform. These instruments support commodity contract collateral obligations and other transactions. As of March 31, 2021, standby letters of credit totaled $5.2 million and would have expired in 2021, subsequently in April of 2021 an extension was effective that reset the expiration dates to 2022. As of March 31, 2021, surety bonds expiring through 2022 totaled $16 million. The underlying liabilities insured by these instruments are reflected on our balance sheets, where applicable. Therefore, no additional liability is reflected for the letters of credit and surety bonds themselves. We enter into agreements that include indemnification provisions relating to liabilities arising from or related to certain of our agreements. Most significantly, APS has agreed to indemnify the equity participants and other parties in the Palo Verde sale leaseback transactions with respect to certain tax matters. Generally, a maximum obligation is not explicitly stated in the indemnification provisions and, therefore, the overall maximum amount of the obligation under such indemnification provisions cannot be reasonably estimated. Based on historical experience and evaluation of the specific indemnities, we do not believe that any material loss related to such indemnification provisions is likely. Pinnacle West has issued parental guarantees and has provided indemnification under certain surety bonds for APS which were not material at March 31, 2021. In connection with the sale of 4CA’s 7% interest to NTEC, Pinnacle West is guaranteeing certain obligations that NTEC will have to the other owners of Four Corners. (See “Four Corners — 4CA Matter” above for information related to this guarantee). Pinnacle West has not needed to perform under this guarantee. A maximum obligation is not explicitly stated in the guarantee and, therefore, the overall maximum amount of the obligation under such guarantee cannot be reasonably estimated; however, we consider the fair value of this guarantee, including expected credit losses, to be immaterial.

Other Income and Other Expense

Other Income and Other Expense3 Months Ended
Mar. 31, 2021
Other Income and Expenses [Abstract]
Other Income and Other ExpenseOther Income and Other Expense The following table pro vides detail of Pinnacle West’s Consolidated other income and other expense (dollars in thousands): Three Months Ended 2021 2020 Other income: Interest income $ 1,948 $ 3,277 Debt return on Four Corners SCR deferrals (Note 4) 4,086 3,140 Debt return on Ocotillo modernization project (Note 4) 6,392 6,144 Miscellaneous 3 8 Total other income $ 12,429 $ 12,569 Other expense: Non-operating costs (1,937) (2,658) Investment gains (losses) — net (343) 60 Miscellaneous (1,573) (2,186) Total other expense $ (3,853) $ (4,784) Three Months Ended 2021 2020 Other income: Interest income $ 1,481 $ 2,341 Debt return on Four Corners SCR deferrals (Note 4) 4,086 3,140 Debt return on Ocotillo modernization project (Note 4) 6,392 6,144 Miscellaneous 1 8 Total other income $ 11,960 $ 11,633 Other expense: Non-operating costs (1,778) (2,482) Miscellaneous (1,572) (2,186) Total other expense $ (3,350) $ (4,668)

Earnings Per Share

Earnings Per Share3 Months Ended
Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings Per ShareEarnings Per Share The following table presents the calculation of Pinnacle West’s basic and diluted earnings per share (in thousands, except per share amounts): Three Months Ended March 31, 2021 2020 Net income attributable to common shareholders $ 35,641 $ 29,993 Weighted average common shares outstanding — basic 112,829 112,594 Net effect of dilutive securities: Contingently issuable performance shares and restricted stock units 264 268 Weighted average common shares outstanding — diluted 113,093 112,862 Earnings per weighted-average common share outstanding Net income attributable to common shareholders — basic $ 0.32 $ 0.27 Net income attributable to common shareholders — diluted $ 0.32 $ 0.27

Fair Value Measurements

Fair Value Measurements3 Months Ended
Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value MeasurementsFair Value Measurements We classify our assets and liabilities that are carried at fair value within the fair value hierarchy. This hierarchy ranks the quality and reliability of the inputs used to determine fair values, which are then classified and disclosed in one of three categories. The three levels of the fair value hierarchy are: Level 1 — Inputs are unadjusted quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2 — Other significant observable inputs, including quoted prices in active markets for similar assets or liabilities; quoted prices in markets that are not active, and model-derived valuations whose inputs are observable (such as yield curves). Level 3 — Valuation models with significant unobservable inputs that are supported by little or no market activity. Instruments in this category may include long-dated derivative transactions where valuations are unobservable due to the length of the transaction, options, and transactions in locations where observable market data does not exist. The valuation models we employ utilize spot prices, forward prices, historical market data and other factors to forecast future prices. Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Thus, a valuation may be classified in Level 3 even though the valuation may include significant inputs that are readily observable. We maximize the use of observable inputs and minimize the use of unobservable inputs. We rely primarily on the market approach of using prices and other market information for identical and/or comparable assets and liabilities. If market data is not readily available, inputs may reflect our own assumptions about the inputs market participants would use. Our assessment of the inputs and the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of fair value assets and liabilities as well as their placement within the fair value hierarchy levels. We assess whether a market is active by obtaining observable broker quotes, reviewing actual market activity, and assessing the volume of transactions. We consider broker quotes observable inputs when the quote is binding on the broker, we can validate the quote with market activity, or we can determine that the inputs the broker used to arrive at the quoted price are observable. Certain instruments have been valued using the concept of Net Asset Value (“NAV”) as a practical expedient. These instruments are typically structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. These instruments are similar to mutual funds; however, their NAV is generally not published and publicly available, nor are these instruments traded on an exchange. Instruments valued using NAV as a practical expedient are included in our fair value disclosures; however, in accordance with GAAP are not classified within the fair value hierarchy levels. Recurring Fair Value Measurements We apply recurring fair value measurements to cash equivalents, derivative instruments, and investments held in the nuclear decommissioning trusts and other special use funds. On an annual basis, we apply fair value measurements to plan assets held in our retirement and other benefit plans. See Note 8 in the 2020 Form 10-K for fair value discussion of plan assets held in our retirement and other benefit plans. Cash Equivalents Cash equivalents represent certain investments in money market funds that are valued using quoted prices in active markets. Risk Management Activities — Derivative Instruments Exchange traded commodity contracts are valued using unadjusted quoted prices. For non-exchange traded commodity contracts, we calculate fair value based on the average of the bid and offer price, discounted to reflect net present value. We maintain certain valuation adjustments for a number of risks associated with the valuation of future commitments. These include valuation adjustments for liquidity and credit risks. The liquidity valuation adjustment represents the cost that would be incurred if all unmatched positions were closed out or hedged. The credit valuation adjustment represents estimated credit losses on our net exposure to counterparties, taking into account netting agreements, expected default experience for the credit rating of the counterparties and the overall diversification of the portfolio. We maintain credit policies that management believes minimize overall credit risk. Certain non-exchange traded commodity contracts are valued based on unobservable inputs due to the long-term nature of contracts, characteristics of the product, or the unique location of the transactions. Our long-dated energy transactions consist of observable valuations for the near-term portion and unobservable valuations for the long-term portions of the transaction. We rely primarily on broker quotes to value these instruments. When our valuations utilize broker quotes, we perform various control procedures to ensure the quote has been developed consistent with fair value accounting guidance. These controls include assessing the quote for reasonableness by comparison against other broker quotes, reviewing historical price relationships, and assessing market activity. When broker quotes are not available, the primary valuation technique used to calculate the fair value is the extrapolation of forward pricing curves using observable market data for more liquid delivery points in the same region and actual transactions at more illiquid delivery points. When the unobservable portion is significant to the overall valuation of the transaction, the entire transaction is classified as Level 3. Investments Held in Nuclear Decommissioning Trusts and Other Special Use Funds The nuclear decommissioning trusts and other special use funds invest in fixed income and equity securities. Other special use funds include the coal reclamation escrow account and the active union employee medical account. See Note 12 for additional discussion about our investment accounts. We value investments in fixed income and equity securities using information provided by our trustees and escrow agent. Our trustees and escrow agent use pricing services that utilize the valuation methodologies described below to determine fair market value. We have internal control procedures designed to ensure this information is consistent with fair value accounting guidance. These procedures include assessing valuations using an independent pricing source, verifying that pricing can be supported by actual recent market transactions, assessing hierarchy classifications, comparing investment returns with benchmarks, and obtaining and reviewing independent audit reports on the trustees’ and escrow agent’s internal operating controls and valuation processes. Fixed Income Securities Fixed income securities issued by the U.S. Treasury are valued using quoted active market prices and are typically classified as Level 1. Fixed income securities issued by corporations, municipalities, and other agencies, including mortgage-backed instruments, are valued using quoted inactive market prices, quoted active market prices for similar securities, or by utilizing calculations which incorporate observable inputs such as yield curves and spreads relative to such yield curves. These fixed income instruments are classified as Level 2. Whenever possible, multiple market quotes are obtained which enables a cross-check validation. A primary price source is identified based on asset type, class, or issue of securities. Fixed income securities may also include short-term investments in certificates of deposit, variable rate notes, time deposit accounts, U.S. Treasury and Agency obligations, U.S. Treasury repurchase agreements, commercial paper, and other short-term instruments. These instruments are valued using active market prices or utilizing observable inputs described above. Equity Securities The Nuclear Decommissioning Trusts's equity security investments are held indirectly through commingled funds. The commingled funds are valued using the funds’ NAV as a practical expedient. The funds’ NAV is primarily derived from the quoted active market prices of the underlying equity securities held by the funds. We may transact in these commingled funds on a semi-monthly basis at the NAV. The commingled funds are maintained by a bank and hold investments in accordance with the stated objective of tracking the performance of the S&P 500 Index. Because the commingled funds’ shares are offered to a limited group of investors, they are not considered to be traded in an active market. As these instruments are valued using NAV, as a practical expedient, they have not been classified within the fair value hierarchy. The Nuclear Decommissioning Trusts and other special use funds may also hold equity securities that include exchange traded mutual funds and money market accounts for short-term liquidity purposes. These short-term, highly-liquid, investments are valued using active market prices. Fair Value Tables The following table presents the fair value at March 31, 2021 of our assets and liabilities that are measured at fair value on a recurring basis (dollars in thousands): Level 1 Level 2 Level 3 Other Total Assets Risk management activities — derivative instruments: Commodity contracts $ — $ 14,353 $ 15,340 $ (3,882) (a) $ 25,811 Nuclear decommissioning trust: Equity securities 22,160 — — (15,538) (b) 6,622 U.S. commingled equity funds — — — 648,199 (c) 648,199 U.S. Treasury debt 175,707 — — — 175,707 Corporate debt — 143,876 — — 143,876 Mortgage-backed securities — 110,073 — — 110,073 Municipal bonds — 64,479 — — 64,479 Other fixed income — 10,743 — — 10,743 Subtotal nuclear decommissioning trust 197,867 329,171 — 632,661 1,159,699 Other special use funds: Equity securities 19,211 — — 1,401 (b) 20,612 U.S. Treasury debt 323,589 — — — 323,589 Municipal bonds — 13,305 — — 13,305 Subtotal other special use funds 342,800 13,305 — 1,401 357,506 Total assets $ 540,667 $ 356,829 $ 15,340 $ 630,180 $ 1,543,016 Liabilities Risk management activities — derivative instruments: Commodity contracts $ — $ (11,668) $ (924) $ 2,597 (a) $ (9,995) (a) Represents counterparty netting, margin, and collateral. See Note 7. (b) Represents net pending securities sales and purchases. (c) Valued using NAV as a practical expedient and, therefore, are not classified in the fair value hierarchy. The following table presents the fair value at December 31, 2020 of our assets and liabilities that are measured at fair value on a recurring basis (dollars in thousands): Level 1 Level 2 Level 3 Other Total Assets Risk management activities — derivative instruments: Commodity contracts $ — $ 9,016 $ 4 $ (4,271) (a) $ 4,749 Nuclear decommissioning trust: Equity securities 29,796 — — (17,828) (b) 11,968 U.S. commingled equity funds — — — 610,055 (c) 610,055 U.S. Treasury debt 164,514 — — — 164,514 Corporate debt — 149,509 — — 149,509 Mortgage-backed securities — 99,623 — — 99,623 Municipal bonds — 89,705 — — 89,705 Other fixed income — 13,061 — — 13,061 Subtotal nuclear decommissioning trust 194,310 351,898 — 592,227 1,138,435 Other special use funds: Equity securities 37,337 — — 504 (b) 37,841 U.S. Treasury debt 203,220 — — — 203,220 Municipal bonds — 13,448 — — 13,448 Subtotal other special use funds 240,557 13,448 — 504 254,509 Total assets $ 434,867 $ 374,362 $ 4 $ 588,460 $ 1,397,693 Liabilities Risk management activities — derivative instruments: Commodity contracts $ — $ (20,498) $ (1,107) $ 2,986 (a) $ (18,619) (a) Represents counterparty netting, margin, and collateral. See Note 7. (b) Represents net pending securities sales and purchases. (c) Valued using NAV as a practical expedient and, therefore, are not classified in the fair value hierarchy. Fair Value Measurements Classified as Level 3 The significant unobservable inputs used in the fair value measurement of our energy derivative contracts include broker quotes that cannot be validated as an observable input primarily due to the long-term nature of the quote or other characteristics of the product. Significant changes in these inputs in isolation would result in significantly higher or lower fair value measurements. Changes in our derivative contract fair values, including changes relating to unobservable inputs, typically will not impact net income due to regulatory accounting treatment (see Note 4). Because our forward commodity contracts classified as Level 3 are currently in a net purchase position, we would expect price increases of the underlying commodity to result in increases in the net fair value of the related contracts. Conversely, if the price of the underlying commodity decreases, the net fair value of the related contracts would likely decrease. Other unobservable valuation inputs include credit and liquidity reserves which do not have a material impact on our valuations; however, significant changes in these inputs could also result in higher or lower fair value measurements. Financial Instruments Not Carried at Fair Value The carrying value of our short-term borrowings approximate fair value and are classified within Level 2 of the fair value hierarchy. See Note 3 for our long-term debt fair values. The NTEC note receivable related to the sale of 4CA’s interest in Four Corners bears interest at 3.9% per annum and has a book value of $22.7 million as of March 31, 2021 and $27.1 million as of December 31, 2020, as presented on the Condensed Consolidated Balance Sheets. The carrying amount is not materially different from the fair value of the note receivable and is classified within Level 3 of the fair value hierarchy. See Note 8 for more information on 4CA matters.

Investments in Nuclear Decommis

Investments in Nuclear Decommissioning Trusts and Other Special Use Funds3 Months Ended
Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investments in Nuclear Decommissioning Trusts and Other Special Use FundsInvestments in Nuclear Decommissioning Trusts and Other Special Use Funds We have investments in debt and equity securities held in Nuclear Decommissioning Trusts, Coal Reclamation Escrow Account, and an Active Union Employee Medical Account. Investments in debt securities are classified as available-for-sale securities. We record both debt and equity security investments at their fair value on our Condensed Consolidated Balance Sheets. See Note 11 for a discussion of how fair value is determined and the classification of the investments within the fair value hierarchy. The investments in each trust or account are restricted for use and are intended to fund specified costs and activities as further described for each fund below. Nuclear Decommissioning Trusts — APS established external decommissioning trusts in accordance with NRC regulations to fund the future costs APS expects to incur to decommission Palo Verde. Third-party investment managers are authorized to buy and sell securities per stated investment guidelines. The trust funds are invested in fixed income securities and equity securities. Earnings and proceeds from sales and maturities of securities are reinvested in the trusts. Because of the ability of APS to recover decommissioning costs in rates, and in accordance with the regulatory treatment, APS has deferred realized and unrealized gains and losses (including credit losses) in other regulatory liabilities. Coal Reclamation Escrow Account — APS has investments restricted for the future coal mine reclamation funding related to Four Corners. This escrow account is primarily invested in fixed income securities. Earnings and proceeds from sales of securities are reinvested in the escrow account. Because of the ability of APS to recover coal mine reclamation costs in rates, and in accordance with the regulatory treatment, APS has deferred realized and unrealized gains and losses (including credit losses) in other regulatory liabilities. Activities relating to APS coal mine reclamation escrow account investments are included within the other special use funds in the table below. Active Union Employee Medical Account — APS has investments restricted for paying active union employee medical costs. These investments may be used to pay active union employee medical costs incurred in the current and future periods. In 2020 and 2019, APS was reimbursed $14 million and $15 million, respectively, for prior year active union employee medical claims from the active union employee medical account. The account is invested primarily in fixed income securities. In accordance with the ratemaking treatment, APS has deferred the unrealized gains and losses (including credit losses) in other regulatory liabilities. Activities relating to active union employee medical account investments are included within the other special use funds in the table below. On January 4, 2021, an additional $106 million of investments were transferred from APS other postretirement benefit trust assets into the active union employee medical account (see Note 5). APS The following tables present the unrealized gains and losses based on the original cost of the investment and summarizes the fair value of APS’s nuclear decommissioning trusts and other special use fund assets (dollars in thousands): March 31, 2021 Fair Value Total Total Investment Type: Nuclear Decommissioning Trusts Other Special Use Funds Total Equity securities $ 670,359 $ 19,211 $ 689,570 $ 457,442 $ — Available for sale-fixed income securities 504,878 336,894 841,772 (a) 27,338 (3,203) Other (15,538) 1,401 (14,137) (b) — — Total $ 1,159,699 $ 357,506 $ 1,517,205 $ 484,780 $ (3,203) (a) As of March 31, 2021, the amortized cost basis of these available-for-sale investments is $818 million. (b) Represents net pending securities sales and purchases. December 31, 2020 Fair Value Total Total Investment Type: Nuclear Decommissioning Trusts Other Special Use Funds Total Equity securities $ 639,851 $ 37,337 $ 677,188 $ 421,666 $ — Available for sale-fixed income securities 516,412 216,668 733,080 (a) 46,581 (398) Other (17,828) 504 (17,324) (b) — — Total $ 1,138,435 $ 254,509 $ 1,392,944 $ 468,247 $ (398) (a) As of December 31, 2020, the amortized cost basis of these available-for-sale investments is $687 million. (b) Represents net pending securities sales and purchases. The following table sets forth APS’s realized gains and losses relating to the sale and maturity of available-for-sale debt securities and equity securities, and the proceeds from the sale and maturity of these investment securities (dollars in thousands): Three Months Ended March 31, Nuclear Decommissioning Trusts Other Special Use Funds Total 2021 Realized gains $ 2,968 $ — $ 2,968 Realized losses (4,148) — (4,148) Proceeds from the sale of securities (a) 234,728 145,250 379,978 2020 Realized gains $ 3,313 $ — $ 3,313 Realized losses (2,227) — (2,227) Proceeds from the sale of securities (a) 178,196 16,891 195,087 (a) Proceeds are reinvested in the nuclear decommissioning trusts and other special use funds, excluding amounts reimbursed to the Company for active union employee medical claims from the active union employee medical account. Fixed Income Securities Contractual Maturities The fair value of APS’s fixed income securities, summarized by contractual maturities, at March 31, 2021, is as follows (dollars in thousands): Nuclear Decommissioning Trust Coal Reclamation Escrow Account Active Union Employee Medical Account Total Less than one year $ 25,048 $ 26,259 $ 40,469 $ 91,776 1 year – 5 years 147,347 34,936 160,324 342,607 5 years – 10 years 137,479 2,708 63,477 203,664 Greater than 10 years 195,004 8,721 — 203,725 Total $ 504,878 $ 72,624 $ 264,270 $ 841,772

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Loss3 Months Ended
Mar. 31, 2021
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Changes in Accumulated Other Comprehensive LossChanges in Accumulated Other Comprehensive Loss The following table shows the changes in Pinnacle West’s consolidated accumulated other comprehensive loss, including reclassification adjustments, net of tax, by component (dollars in thousands): Pension and Other Postretirement Benefits Derivative Instruments Total Three Months Ended March 31 Balance December 31, 2020 $ (60,725) $ (2,071) $ (62,796) OCI (loss) before reclassifications — 262 262 Amounts reclassified from accumulated other comprehensive loss 1,022 (a) — 1,022 Balance March 31, 2021 $ (59,703) $ (1,809) $ (61,512) Balance December 31, 2019 $ (56,522) $ (574) $ (57,096) OCI (loss) before reclassifications — 292 292 Amounts reclassified from accumulated other comprehensive loss 1,205 (a) 20 (b) 1,225 Balance March 31, 2020 $ (55,317) $ (262) $ (55,579) (a) These amounts primarily represent amortization of actuarial loss and are included in the computation of net periodic pension cost. See Note 5. (b) These amounts primarily represent realized gains and losses and are included in the computation of fuel and purchased power costs and are subject to the PSA. See Note 7. The following table shows the changes in APS’s consolidated accumulated other comprehensive loss, including reclassification adjustments, net of tax, by component for the three months ended March 31, 2021 and 2020 (dollars in thousands): Pension and Other Postretirement Benefits Derivative Instruments Total Three Months Ended March 31 Balance December 31, 2020 $ (40,918) $ — $ (40,918) Amounts reclassified from accumulated other comprehensive loss 927 (a) — 927 Balance March 31, 2021 $ (39,991) $ — $ (39,991) Balance December 31, 2019 $ (34,948) $ (574) $ (35,522) OCI (loss) before reclassifications — 292 292 Amounts reclassified from accumulated other comprehensive loss 1,013 (a) 20 (b) 1,033 Balance March 31, 2020 $ (33,935) $ (262) $ (34,197) (a) These amounts primarily represent amortization of actuarial loss and are included in the computation of net periodic pension cost. See Note 5. (b) These amounts primarily represent realized gains and losses and are included in the computation of fuel and purchased power costs and are subject to the PSA. See Note 7.

Income Taxes

Income Taxes3 Months Ended
Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income TaxesIncome Taxes The Tax Act reduced the corporate tax rate to 21% effective January 1, 2018. As a result of this rate reduction, the Company recognized a $1.14 billion reduction in its net deferred income tax liabilities as of December 31, 2017. In accordance with accounting for regulated companies, the effect of this rate reduction was substantially offset by a net regulatory liability. Federal income tax laws require the amortization of a majority of the balance over the remaining regulatory life of the related property. As a result of the modifications made to the annual transmission formula rate during the second quarter of 2018, the Company began amortization of FERC jurisdictional net excess deferred tax liabilities in 2018. On March 13, 2019, the ACC approved the Company’s proposal to amortize non-depreciation related net excess deferred tax liabilities subject to its jurisdiction over a twelve-month period. As a result, the Company began amortization in March 2019. The Company recorded $14 million of income tax benefit related to the amortization of these non-depreciation related net excess deferred tax liabilities as of March 31, 2020, with these non-depreciation related net excess deferred tax liabilities being fully amortized as of March 31, 2020. On October 29, 2019, the ACC approved the Company’s proposal to amortize depreciation related net excess deferred tax liabilities subject to its jurisdiction over a 28.5-year period with amortization to retroactively begin as of January 1, 2018. The Company recorded $6 million and $6 million of income tax benefit related to amortization of these depreciation related net excess deferred tax liabilities as of March 31, 2021 and March 31, 2020, respectively. See Note 4 for more details. Net income associated with the Palo Verde sale leaseback VIEs is not subject to tax. As a result, there is no income tax expense associated with the VIEs recorded on the Pinnacle West Consolidated and APS Consolidated Statements of Income. See Note 6 for additional details related to the Palo Verde sale leaseback VIEs. As of the balance sheet date, the tax year ended December 31, 2017 and all subsequent tax years remain subject to examination by the IRS. With a few exceptions, the Company is no longer subject to state income tax examinations by tax authorities for years before 2016.

Consolidation and Nature of O_2

Consolidation and Nature of Operations (Tables)3 Months Ended
Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of supplemental cash flow informationThe following table summarizes supplemental Pinnacle West cash flow information (dollars in thousands): Three Months Ended 2021 2020 Cash paid during the period for: Income taxes, net of refunds $ (827) $ (3,002) Interest, net of amounts capitalized 53,885 53,723 Significant non-cash investing and financing activities: Accrued capital expenditures $ 79,597 $ 100,868 Right-of-use operating lease assets obtained in exchange for operating lease liabilities 785 2,311 The following table summarizes supplemental APS cash flow information (dollars in thousands): Three Months Ended 2021 2020 Cash paid during the period for: Income taxes, net of refunds $ — $ — Interest, net of amounts capitalized 53,153 52,034 Significant non-cash investing and financing activities: Accrued capital expenditures $ 79,597 $ 100,868 Right-of-use operating lease assets obtained in exchange for operating lease liabilities 785 2,311

Revenue (Tables)

Revenue (Tables)3 Months Ended
Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of RevenueThe following table provides detail of Pinnacle West’s consolidated revenue disaggregated by revenue sources (dollars in thousands): Three Months Ended March 31, 2021 2020 Retail Electric Revenue Residential $ 340,838 $ 325,073 Non-Residential 314,783 303,351 Wholesale Energy Sales 17,597 14,668 Transmission Services for Others 18,993 15,927 Other Sources 4,264 2,911 Total operating revenues $ 696,475 $ 661,930
Schedule of Accounts ReceivableThe following table provides a rollforward of Pinnacle West’s allowance for doubtful accounts (dollars in thousands): March 31, 2021 December 31, 2020 Allowance for doubtful accounts, balance at beginning of period $ 19,782 $ 8,171 Bad debt expense 4,151 20,633 Actual write-offs (3,528) (9,022) Allowance for doubtful accounts, balance at end of period $ 20,405 $ 19,782

Long-Term Debt and Liquidity _2

Long-Term Debt and Liquidity Matters (Tables)3 Months Ended
Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of estimated fair value of long-term debt, including current maturitiesThe following table presents the estimated fair value of our long-term debt, including current maturities (dollars in thousands): As of March 31, 2021 As of December 31, 2020 Carrying Fair Value Carrying Fair Value Pinnacle West $ 646,525 $ 653,395 $ 496,321 $ 509,050 APS 5,818,520 6,436,224 5,817,945 7,103,791 Total $ 6,465,045 $ 7,089,619 $ 6,314,266 $ 7,612,841

Regulatory Matters (Tables)

Regulatory Matters (Tables)3 Months Ended
Mar. 31, 2021
Regulated Operations [Abstract]
Schedule of capital structure and cost of capitalthe following proposed capital structure and costs of capital: Capital Structure Cost of Capital Long-term debt 45.3 % 4.10 % Common stock equity 54.7 % 10.15 % Weighted-average cost of capital 7.41 %
Schedule of changes in the deferred fuel and purchased power regulatory assetThe following table shows the changes in the deferred fuel and purchased power regulatory asset for 2021 and 2020 (dollars in thousands): Three Months Ended 2021 2020 Beginning balance $ 175,835 $ 70,137 Deferred fuel and purchased power costs — current period 52,210 5,785 Amounts refunded to customers 564 1,808 Ending balance $ 228,609 $ 77,730
Schedule of regulatory assetsThe detail of regulatory assets is as follows (dollars in thousands): Amortization Through March 31, 2021 December 31, 2020 Current Non-Current Current Non-Current Pension (a) $ — $ 467,423 $ — $ 469,953 Deferred fuel and purchased power (b) (c) 2022 228,609 — 175,835 — Income taxes — allowance for funds used during construction (“AFUDC”) equity 2051 7,169 159,119 7,169 158,776 Retired power plant costs 2033 28,182 107,169 28,181 114,214 Ocotillo deferral N/A — 110,820 — 95,723 SCR deferral N/A — 88,044 — 81,307 Deferred property taxes 2027 8,569 47,484 8,569 49,626 Lost fixed cost recovery (b) 2022 45,905 — 41,807 — Deferred compensation 2036 — 35,806 — 36,195 Four Corners cost deferral 2024 8,077 22,056 8,077 24,075 Income taxes — investment tax credit basis adjustment 2049 1,113 24,221 1,113 24,291 Palo Verde VIEs (Note 6) 2046 — 21,409 — 21,255 Coal reclamation 2026 1,068 16,732 1,068 16,999 Loss on reacquired debt 2038 1,703 10,486 1,689 10,877 Mead-Phoenix transmission line contributions in aid of construction (“CIAC”) 2050 332 9,297 332 9,380 Demand side management (b) 2021 — 7,268 — 7,268 Tax expense adjustor mechanism (b) 2021 5,854 — 6,226 — Tax expense of Medicare subsidy 2024 1,235 3,626 1,235 3,704 Deferred fuel and purchased power — mark-to-market (Note 7) 2024 — 3,728 3,341 9,244 PSA interest 2022 46 — 4,355 — Other Various 2,018 1,169 2,716 1,100 Total regulatory assets (d) $ 339,880 $ 1,135,857 $ 291,713 $ 1,133,987 (a) This asset represents the future recovery of pension benefit obligations through retail rates. If these costs are disallowed by the ACC, this regulatory asset would be charged to other comprehensive income (“OCI”) and result in lower future revenues. See Note 5. (b) See “Cost Recovery Mechanisms” discussion above. (c) Subject to a carrying charge. (d) There are no regulatory assets for which the ACC has allowed recovery of costs, but not allowed a return by exclusion from rate base. FERC rates are set using a formula rate as described in “Transmission Rates, Transmission Cost Adjustor and Other Transmission Matters.”
Schedule of regulatory liabilitiesThe detail of regulatory liabilities is as follows (dollars in thousands): Amortization Through March 31, 2021 December 31, 2020 Current Non-Current Current Non-Current Excess deferred income taxes - ACC - Tax Cuts and Jobs Act (a) 2046 $ 41,353 $ 1,004,226 $ 41,330 $ 1,012,583 Excess deferred income taxes - FERC - Tax Cuts and Jobs Act (a) 2058 7,240 228,690 7,240 229,147 Asset retirement obligations 2057 — 519,015 — 506,049 Other postretirement benefits (d) 37,705 337,853 37,705 349,588 Removal costs (c) 55,247 89,937 52,844 103,008 Income taxes — change in rates 2050 2,839 66,374 2,839 66,553 Four Corners coal reclamation 2038 5,461 49,703 5,460 49,435 Income taxes — deferred investment tax credit 2049 2,231 48,507 2,231 48,648 Spent nuclear fuel 2027 6,831 43,059 6,768 44,221 Renewable energy standard (b) 2022 34,460 30 39,442 103 Deferred fuel and purchased power — mark-to-market (Note 7) 2022 20,829 — — — Property tax deferral N/A — 15,022 — 13,856 Sundance maintenance 2031 2,867 11,910 2,989 11,508 Demand side management (b) 2022 7,821 5,975 10,819 — FERC transmission true up 2023 7,630 2,379 6,598 3,008 TCA balancing account (b) 2022 7,315 1,754 2,902 4,672 Tax expense adjustor mechanism (b) (e) 2021 7,452 — 7,089 — Deferred gains on utility property 2022 2,423 939 2,423 1,544 Active union medical trust N/A — 2,337 — 6,057 Other Various 524 59 409 189 Total regulatory liabilities $ 250,228 $ 2,427,769 $ 229,088 $ 2,450,169 (a) For purposes of presentation on the Statement of Cash Flows, amortization of the regulatory liabilities for excess deferred income taxes are reflected as “Deferred income taxes” under Cash Flows From Operating Activities. (b) See “Cost Recovery Mechanisms” discussion above. (c) In accordance with regulatory accounting guidance, APS accrues removal costs for its regulated assets, even if there is no legal obligation for removal. (d) See Note 5. (e) Pursuant to Decision 77852, the ACC has authorized APS to return to customers up to $7 million of liability recorded to the TEAM balancing account through December 31, 2021. Should new base rates become effective prior to December 31, 2021, any remaining unreturned balance is anticipated to be included in the new base rates.

Retirement Plans and Other Po_2

Retirement Plans and Other Postretirement Benefits (Tables)3 Months Ended
Mar. 31, 2021
Retirement Benefits [Abstract]
Schedule of net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction, billed to electric plant participants or charged or amortized to the regulatory asset)The following table provides details of the plans’ net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction or billed to electric plant participants) (dollars in thousands): Pension Benefits Other Benefits Three Months Ended Three Months Ended 2021 2020 2021 2020 Service cost — benefits earned during the period $ 15,679 $ 14,257 $ 4,557 $ 5,717 Non-service costs (credits): Interest cost on benefit obligation 24,669 29,761 4,162 6,512 Expected return on plan assets (50,608) (46,806) (10,361) (10,019) Amortization of: Prior service credit — — (9,427) (9,394) Net actuarial loss (gain) 3,985 9,011 (2,405) — Net periodic benefit cost/(benefit) $ (6,275) $ 6,223 $ (13,474) $ (7,184) Portion of cost/(benefit) charged to expense $ (8,011) $ 1,342 $ (9,528) $ (5,456)

Palo Verde Sale Leaseback Var_2

Palo Verde Sale Leaseback Variable Interest Entities (Tables)3 Months Ended
Mar. 31, 2021
Variable Interest Entities [Abstract]
Amounts relating to the VIEs included in Condensed Consolidated Balance SheetsOur Condensed Consolidated Balance Sheets at March 31, 2021 and December 31, 2020 include the following amounts relating to the VIEs (dollars in thousands): March 31, 2021 December 31, 2020 Palo Verde sale leaseback property, plant and equipment, net of accumulated depreciation $ 97,068 $ 98,036 Equity — Noncontrolling interests 124,164 119,290

Derivative Accounting (Tables)

Derivative Accounting (Tables)3 Months Ended
Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Outstanding gross notional amount of derivatives, which represents both purchases and sales (does not reflect net position)The following table shows the outstanding gross notional volume of derivatives, which represent both purchases and sales (does not reflect net position): Quantity Commodity Unit of Measure March 31, 2021 December 31, 2020 Power GWh 368 368 Gas Billion cubic feet 211 205
Gains and losses from derivative instruments in designated cash flow accounting hedges relationshipsThe following table provides information about APS’s gains and losses from derivative instruments in designated cash flow accounting hedging relationships (dollars in thousands): Financial Statement Location Three Months Ended Commodity Contracts 2021 2020 Loss Reclassified from Accumulated OCI into Income (Effective Portion Realized) (a) Fuel and purchased power (b) $ — $ (414) (a) During the three months ended March 31, 2021 and 2020, we had no gains or losses reclassified from accumulated OCI to earnings related to discontinued cash flow hedges . (b) Amounts are before the effect of PSA deferrals.
Gains and losses from derivative instruments not designated as accounting hedges instrumentsThe following table provides information about gains and losses from derivative instruments not designated as accounting hedging instruments (dollars in thousands): Financial Statement Location Three Months Ended Commodity Contracts 2021 2020 Net Gain (Loss) Recognized in Income Fuel and purchased power (a) $ 26,859 $ (30,078) (a) Amounts are before the effect of PSA deferrals.
Schedule of offsetting assetsThe following tables provide information about the fair value of our risk management activities reported on a gross basis and the impacts of offsetting. These amounts relate to commodity contracts and are located in the assets and liabilities from risk management activities and other assets lines of our Condensed Consolidated Balance Sheets. As of March 31, 2021: Gross Recognized Derivatives (a) Amounts Net Recognized Derivatives Other (c) Amount Reported on Balance Sheet Current assets $ 25,703 $ (3,092) $ 22,611 $ — $ 22,611 Investments and other assets 3,990 (790) 3,200 — 3,200 Total assets 29,693 (3,882) 25,811 — 25,811 Current liabilities (4,874) 3,092 (1,782) (1,285) (3,067) Deferred credits and other (7,718) 790 (6,928) — (6,928) Total liabilities (12,592) 3,882 (8,710) (1,285) (9,995) Total $ 17,101 $ — $ 17,101 $ (1,285) $ 15,816 (a) All of our gross recognized derivative instruments were subject to master netting arrangements. (b) No cash collateral has been provided to counterparties, or received from counterparties, that is subject to offsetting. (c) Represents cash collateral that is not subject to offsetting. Amounts relate to non-derivative instruments, derivatives qualifying for scope exceptions or collateral posted in excess of the recognized derivative instrument. Includes cash collateral received from counterparties of $1,285. As of December 31, 2020: Gross Recognized Derivatives (a) Amounts Net Recognized Derivatives Other (c) Amount Current assets $ 5,870 $ (2,939) $ 2,931 $ — $ 2,931 Investments and other assets 3,150 (1,332) 1,818 — 1,818 Total assets 9,020 (4,271) 4,749 — 4,749 Current liabilities (9,211) 2,939 (6,272) (1,285) (7,557) Deferred credits and other (12,394) 1,332 (11,062) — (11,062) Total liabilities (21,605) 4,271 (17,334) (1,285) (18,619) Total $ (12,585) $ — $ (12,585) $ (1,285) $ (13,870) (a) All of our gross recognized derivative instruments were subject to master netting arrangements. (b) No cash collateral has been provided to counterparties, or received from counterparties, that is subject to offsetting. (c) Represents cash collateral and cash margin that is not subject to offsetting. Amounts relate to non-derivative instruments, derivatives qualifying for scope exceptions, or collateral and margin posted in excess of the recognized derivative instrument. Includes cash collateral received from counterparties of $1,285.
Schedule of offsetting liabilitiesThe following tables provide information about the fair value of our risk management activities reported on a gross basis and the impacts of offsetting. These amounts relate to commodity contracts and are located in the assets and liabilities from risk management activities and other assets lines of our Condensed Consolidated Balance Sheets. As of March 31, 2021: Gross Recognized Derivatives (a) Amounts Net Recognized Derivatives Other (c) Amount Reported on Balance Sheet Current assets $ 25,703 $ (3,092) $ 22,611 $ — $ 22,611 Investments and other assets 3,990 (790) 3,200 — 3,200 Total assets 29,693 (3,882) 25,811 — 25,811 Current liabilities (4,874) 3,092 (1,782) (1,285) (3,067) Deferred credits and other (7,718) 790 (6,928) — (6,928) Total liabilities (12,592) 3,882 (8,710) (1,285) (9,995) Total $ 17,101 $ — $ 17,101 $ (1,285) $ 15,816 (a) All of our gross recognized derivative instruments were subject to master netting arrangements. (b) No cash collateral has been provided to counterparties, or received from counterparties, that is subject to offsetting. (c) Represents cash collateral that is not subject to offsetting. Amounts relate to non-derivative instruments, derivatives qualifying for scope exceptions or collateral posted in excess of the recognized derivative instrument. Includes cash collateral received from counterparties of $1,285. As of December 31, 2020: Gross Recognized Derivatives (a) Amounts Net Recognized Derivatives Other (c) Amount Current assets $ 5,870 $ (2,939) $ 2,931 $ — $ 2,931 Investments and other assets 3,150 (1,332) 1,818 — 1,818 Total assets 9,020 (4,271) 4,749 — 4,749 Current liabilities (9,211) 2,939 (6,272) (1,285) (7,557) Deferred credits and other (12,394) 1,332 (11,062) — (11,062) Total liabilities (21,605) 4,271 (17,334) (1,285) (18,619) Total $ (12,585) $ — $ (12,585) $ (1,285) $ (13,870) (a) All of our gross recognized derivative instruments were subject to master netting arrangements. (b) No cash collateral has been provided to counterparties, or received from counterparties, that is subject to offsetting. (c) Represents cash collateral and cash margin that is not subject to offsetting. Amounts relate to non-derivative instruments, derivatives qualifying for scope exceptions, or collateral and margin posted in excess of the recognized derivative instrument. Includes cash collateral received from counterparties of $1,285.
Information about derivative instruments that have credit-risk-related contingent featuresThe following table provides information about our derivative instruments that have credit-risk-related contingent features (dollars in thousands): March 31, 2021 Aggregate fair value of derivative instruments in a net liability position $ 11,520 Cash collateral posted — Additional cash collateral in the event credit-risk-related contingent features were fully triggered (a) 6,674 (a) This amount is after counterparty netting and includes those contracts which qualify for scope exceptions, which are excluded from the derivative details above.

Other Income and Other Expense

Other Income and Other Expense (Tables)3 Months Ended
Mar. 31, 2021
Other Income and Expenses [Abstract]
Detail of other income and other expenseThe following table pro vides detail of Pinnacle West’s Consolidated other income and other expense (dollars in thousands): Three Months Ended 2021 2020 Other income: Interest income $ 1,948 $ 3,277 Debt return on Four Corners SCR deferrals (Note 4) 4,086 3,140 Debt return on Ocotillo modernization project (Note 4) 6,392 6,144 Miscellaneous 3 8 Total other income $ 12,429 $ 12,569 Other expense: Non-operating costs (1,937) (2,658) Investment gains (losses) — net (343) 60 Miscellaneous (1,573) (2,186) Total other expense $ (3,853) $ (4,784) Three Months Ended 2021 2020 Other income: Interest income $ 1,481 $ 2,341 Debt return on Four Corners SCR deferrals (Note 4) 4,086 3,140 Debt return on Ocotillo modernization project (Note 4) 6,392 6,144 Miscellaneous 1 8 Total other income $ 11,960 $ 11,633 Other expense: Non-operating costs (1,778) (2,482) Miscellaneous (1,572) (2,186) Total other expense $ (3,350) $ (4,668)

Earnings Per Share (Tables)

Earnings Per Share (Tables)3 Months Ended
Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of earnings per weighted average common share outstandingThe following table presents the calculation of Pinnacle West’s basic and diluted earnings per share (in thousands, except per share amounts): Three Months Ended March 31, 2021 2020 Net income attributable to common shareholders $ 35,641 $ 29,993 Weighted average common shares outstanding — basic 112,829 112,594 Net effect of dilutive securities: Contingently issuable performance shares and restricted stock units 264 268 Weighted average common shares outstanding — diluted 113,093 112,862 Earnings per weighted-average common share outstanding Net income attributable to common shareholders — basic $ 0.32 $ 0.27 Net income attributable to common shareholders — diluted $ 0.32 $ 0.27

Fair Value Measurements (Tables

Fair Value Measurements (Tables)3 Months Ended
Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair value of assets and liabilities that are measured at fair value on a recurring basisThe following table presents the fair value at March 31, 2021 of our assets and liabilities that are measured at fair value on a recurring basis (dollars in thousands): Level 1 Level 2 Level 3 Other Total Assets Risk management activities — derivative instruments: Commodity contracts $ — $ 14,353 $ 15,340 $ (3,882) (a) $ 25,811 Nuclear decommissioning trust: Equity securities 22,160 — — (15,538) (b) 6,622 U.S. commingled equity funds — — — 648,199 (c) 648,199 U.S. Treasury debt 175,707 — — — 175,707 Corporate debt — 143,876 — — 143,876 Mortgage-backed securities — 110,073 — — 110,073 Municipal bonds — 64,479 — — 64,479 Other fixed income — 10,743 — — 10,743 Subtotal nuclear decommissioning trust 197,867 329,171 — 632,661 1,159,699 Other special use funds: Equity securities 19,211 — — 1,401 (b) 20,612 U.S. Treasury debt 323,589 — — — 323,589 Municipal bonds — 13,305 — — 13,305 Subtotal other special use funds 342,800 13,305 — 1,401 357,506 Total assets $ 540,667 $ 356,829 $ 15,340 $ 630,180 $ 1,543,016 Liabilities Risk management activities — derivative instruments: Commodity contracts $ — $ (11,668) $ (924) $ 2,597 (a) $ (9,995) (a) Represents counterparty netting, margin, and collateral. See Note 7. (b) Represents net pending securities sales and purchases. (c) Valued using NAV as a practical expedient and, therefore, are not classified in the fair value hierarchy. The following table presents the fair value at December 31, 2020 of our assets and liabilities that are measured at fair value on a recurring basis (dollars in thousands): Level 1 Level 2 Level 3 Other Total Assets Risk management activities — derivative instruments: Commodity contracts $ — $ 9,016 $ 4 $ (4,271) (a) $ 4,749 Nuclear decommissioning trust: Equity securities 29,796 — — (17,828) (b) 11,968 U.S. commingled equity funds — — — 610,055 (c) 610,055 U.S. Treasury debt 164,514 — — — 164,514 Corporate debt — 149,509 — — 149,509 Mortgage-backed securities — 99,623 — — 99,623 Municipal bonds — 89,705 — — 89,705 Other fixed income — 13,061 — — 13,061 Subtotal nuclear decommissioning trust 194,310 351,898 — 592,227 1,138,435 Other special use funds: Equity securities 37,337 — — 504 (b) 37,841 U.S. Treasury debt 203,220 — — — 203,220 Municipal bonds — 13,448 — — 13,448 Subtotal other special use funds 240,557 13,448 — 504 254,509 Total assets $ 434,867 $ 374,362 $ 4 $ 588,460 $ 1,397,693 Liabilities Risk management activities — derivative instruments: Commodity contracts $ — $ (20,498) $ (1,107) $ 2,986 (a) $ (18,619) (a) Represents counterparty netting, margin, and collateral. See Note 7. (b) Represents net pending securities sales and purchases. (c) Valued using NAV as a practical expedient and, therefore, are not classified in the fair value hierarchy.

Investments in Nuclear Decomm_2

Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Tables)3 Months Ended
Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Fair value of APS's nuclear decommissioning trust fund assetsThe following tables present the unrealized gains and losses based on the original cost of the investment and summarizes the fair value of APS’s nuclear decommissioning trusts and other special use fund assets (dollars in thousands): March 31, 2021 Fair Value Total Total Investment Type: Nuclear Decommissioning Trusts Other Special Use Funds Total Equity securities $ 670,359 $ 19,211 $ 689,570 $ 457,442 $ — Available for sale-fixed income securities 504,878 336,894 841,772 (a) 27,338 (3,203) Other (15,538) 1,401 (14,137) (b) — — Total $ 1,159,699 $ 357,506 $ 1,517,205 $ 484,780 $ (3,203) (a) As of March 31, 2021, the amortized cost basis of these available-for-sale investments is $818 million. (b) Represents net pending securities sales and purchases. December 31, 2020 Fair Value Total Total Investment Type: Nuclear Decommissioning Trusts Other Special Use Funds Total Equity securities $ 639,851 $ 37,337 $ 677,188 $ 421,666 $ — Available for sale-fixed income securities 516,412 216,668 733,080 (a) 46,581 (398) Other (17,828) 504 (17,324) (b) — — Total $ 1,138,435 $ 254,509 $ 1,392,944 $ 468,247 $ (398) (a) As of December 31, 2020, the amortized cost basis of these available-for-sale investments is $687 million. (b) Represents net pending securities sales and purchases.
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust fundsThe following table sets forth APS’s realized gains and losses relating to the sale and maturity of available-for-sale debt securities and equity securities, and the proceeds from the sale and maturity of these investment securities (dollars in thousands): Three Months Ended March 31, Nuclear Decommissioning Trusts Other Special Use Funds Total 2021 Realized gains $ 2,968 $ — $ 2,968 Realized losses (4,148) — (4,148) Proceeds from the sale of securities (a) 234,728 145,250 379,978 2020 Realized gains $ 3,313 $ — $ 3,313 Realized losses (2,227) — (2,227) Proceeds from the sale of securities (a) 178,196 16,891 195,087
Fair value of fixed income securities, summarized by contractual maturitiesThe fair value of APS’s fixed income securities, summarized by contractual maturities, at March 31, 2021, is as follows (dollars in thousands): Nuclear Decommissioning Trust Coal Reclamation Escrow Account Active Union Employee Medical Account Total Less than one year $ 25,048 $ 26,259 $ 40,469 $ 91,776 1 year – 5 years 147,347 34,936 160,324 342,607 5 years – 10 years 137,479 2,708 63,477 203,664 Greater than 10 years 195,004 8,721 — 203,725 Total $ 504,878 $ 72,624 $ 264,270 $ 841,772

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Loss (Tables)3 Months Ended
Mar. 31, 2021
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Schedule of changes in accumulated other comprehensive loss including reclassification adjustments, net of tax, by componentThe following table shows the changes in Pinnacle West’s consolidated accumulated other comprehensive loss, including reclassification adjustments, net of tax, by component (dollars in thousands): Pension and Other Postretirement Benefits Derivative Instruments Total Three Months Ended March 31 Balance December 31, 2020 $ (60,725) $ (2,071) $ (62,796) OCI (loss) before reclassifications — 262 262 Amounts reclassified from accumulated other comprehensive loss 1,022 (a) — 1,022 Balance March 31, 2021 $ (59,703) $ (1,809) $ (61,512) Balance December 31, 2019 $ (56,522) $ (574) $ (57,096) OCI (loss) before reclassifications — 292 292 Amounts reclassified from accumulated other comprehensive loss 1,205 (a) 20 (b) 1,225 Balance March 31, 2020 $ (55,317) $ (262) $ (55,579) (a) These amounts primarily represent amortization of actuarial loss and are included in the computation of net periodic pension cost. See Note 5. (b) These amounts primarily represent realized gains and losses and are included in the computation of fuel and purchased power costs and are subject to the PSA. See Note 7. The following table shows the changes in APS’s consolidated accumulated other comprehensive loss, including reclassification adjustments, net of tax, by component for the three months ended March 31, 2021 and 2020 (dollars in thousands): Pension and Other Postretirement Benefits Derivative Instruments Total Three Months Ended March 31 Balance December 31, 2020 $ (40,918) $ — $ (40,918) Amounts reclassified from accumulated other comprehensive loss 927 (a) — 927 Balance March 31, 2021 $ (39,991) $ — $ (39,991) Balance December 31, 2019 $ (34,948) $ (574) $ (35,522) OCI (loss) before reclassifications — 292 292 Amounts reclassified from accumulated other comprehensive loss 1,013 (a) 20 (b) 1,033 Balance March 31, 2020 $ (33,935) $ (262) $ (34,197) (a) These amounts primarily represent amortization of actuarial loss and are included in the computation of net periodic pension cost. See Note 5. (b) These amounts primarily represent realized gains and losses and are included in the computation of fuel and purchased power costs and are subject to the PSA. See Note 7.

Consolidation and Nature of O_3

Consolidation and Nature of Operations (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Cash paid during the period for:
Income taxes, net of refunds $ (827) $ (3,002)
Interest, net of amounts capitalized53,885 53,723
Significant non-cash investing and financing activities:
Accrued capital expenditures79,597 100,868
Right-of-use operating lease assets obtained in exchange for operating lease liabilities785 2,311
APS
Cash paid during the period for:
Income taxes, net of refunds0 0
Interest, net of amounts capitalized53,153 52,034
Significant non-cash investing and financing activities:
Accrued capital expenditures79,597 100,868
Right-of-use operating lease assets obtained in exchange for operating lease liabilities $ 785 $ 2,311

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Operating revenues $ 696,475 $ 661,930
Regulatory cost recovery revenue14,000 14,000
Electric Service | Residential
Disaggregation of Revenue [Line Items]
Operating revenues340,838 325,073
Electric Service | Non-Residential
Disaggregation of Revenue [Line Items]
Operating revenues314,783 303,351
Electric Service | Wholesale Energy Sales
Disaggregation of Revenue [Line Items]
Operating revenues17,597 14,668
Transmission Services for Others
Disaggregation of Revenue [Line Items]
Operating revenues18,993 15,927
Other Sources
Disaggregation of Revenue [Line Items]
Operating revenues4,264 2,911
Electric and Transmission Service
Disaggregation of Revenue [Line Items]
Operating revenues $ 682,000 $ 648,000

Revenue - Allowance for Doubtfu

Revenue - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands3 Months Ended12 Months Ended
Mar. 31, 2021Dec. 31, 2020Mar. 31, 2021
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for doubtful accounts, balance at beginning of period $ 19,782 $ 8,171
Bad debt expense4,151 20,633
Actual write-offs(3,528)(9,022)
Allowance for doubtful accounts, balance at end of period $ 19,782 $ 8,171 $ 20,405

Long-Term Debt and Liquidity _3

Long-Term Debt and Liquidity Matters - Narrative (Details)May 04, 2021USD ($)Mar. 31, 2021USD ($)FacilityMar. 31, 2020USD ($)Dec. 23, 2020USD ($)Dec. 17, 2020USD ($)May 05, 2020USD ($)May 04, 2020USD ($)
Long-Term Debt and Liquidity Matters
Repayments of lines of credit $ 4,000,000 $ 226,690,000
Percentage of capitalization7.00%
Capacity available for trade purchases $ 500,000,000
Term Loan
Long-Term Debt and Liquidity Matters
Debt instrument, face amount $ 150,000,000
Pinnacle West | Revolving Credit Facility | Revolving credit Facility maturing July 2023
Long-Term Debt and Liquidity Matters
Long-term line of credit0
Current borrowing capacity on credit facility200,000,000
Maximum borrowing capacity on credit facility upon satisfaction of certain conditions and consent of lenders (up to)300,000,000
Pinnacle West | Letter of Credit | Revolving credit Facility maturing July 2023
Long-Term Debt and Liquidity Matters
Outstanding letters of credit0
Pinnacle West | Commercial paper | Revolving credit Facility maturing July 2023
Long-Term Debt and Liquidity Matters
Commercial paper $ 300,000
Pinnacle West | Term Loan
Long-Term Debt and Liquidity Matters
Debt instrument, face amount $ 31,000,000 $ 50,000,000
Variable rate1.40%
Long-term line of credit $ 15,000,000
Pinnacle West | Term Loan | Subsequent Event
Long-Term Debt and Liquidity Matters
Repayments of lines of credit $ 15,000,000
APS
Long-Term Debt and Liquidity Matters
Repayments of lines of credit0 $ 110,000,000
Long-term debt limit $ 7,500,000,000
APS | Revolving Credit Facility | Revolving credit Facility maturing July 2023
Long-Term Debt and Liquidity Matters
Current borrowing capacity on credit facility500,000,000
Maximum borrowing capacity on credit facility upon satisfaction of certain conditions and consent of lenders (up to)700,000,000
APS | Revolving Credit Facility | Revolving Credit Facility Maturing in 2022 and 2023
Long-Term Debt and Liquidity Matters
Long-term line of credit0
Current borrowing capacity on credit facility1,000,000,000
Maximum borrowing capacity on credit facility upon satisfaction of certain conditions and consent of lenders (up to) $ 1,400,000,000
Number of line of credit facilities | Facility2
APS | Revolving Credit Facility | Revolving credit facility maturing June 2022
Long-Term Debt and Liquidity Matters
Current borrowing capacity on credit facility $ 500,000,000
Maximum borrowing capacity on credit facility upon satisfaction of certain conditions and consent of lenders (up to)700,000,000
APS | Letter of Credit | Revolving Credit Facility Maturing in 2022 and 2023
Long-Term Debt and Liquidity Matters
Outstanding letters of credit0
APS | Commercial paper
Long-Term Debt and Liquidity Matters
Maximum commercial paper support available under credit facility750,000,000
APS | Commercial paper | Revolving Credit Facility Maturing in 2022 and 2023
Long-Term Debt and Liquidity Matters
Commercial paper $ 199,500,000

Long-Term Debt and Liquidity _4

Long-Term Debt and Liquidity Matters - Estimated Fair Value of Long-Term Debt (Details) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Estimated fair value of long-term debt, including current maturities
Carrying Amount $ 6,465,045 $ 6,314,266
Fair Value7,089,619 7,612,841
APS
Estimated fair value of long-term debt, including current maturities
Carrying Amount5,818,520 5,817,945
Fair Value6,436,224 7,103,791
Pinnacle West
Estimated fair value of long-term debt, including current maturities
Carrying Amount646,525 496,321
Fair Value $ 653,395 $ 509,050

Regulatory Matters - COVID-19 (

Regulatory Matters - COVID-19 (Details) - APS - USD ($)Jan. 21, 2021Mar. 31, 2021Dec. 31, 2020May 05, 2020
Public Utilities, General Disclosures [Line Items]
Percentage increase under PSA effective for first billing cycle beginning April 202150.00%
Remaining percentage increase under PSA effective for first billing cycle beginning November 202150.00%
Demand side management funds $ 36,000,000
Customer credits $ 43,000,000
Customer credits, additional funds $ 7,000,000
Voluntary funds $ 15,000,000
Customer COVID assistance12,400,000
Non-customer funds8,800,000
Bill credits for limited income customers $ 3,600,000
Threshold percentage for deferral of potential recovery50.00%
Threshold for deferral of potential recovery $ 2,500,000
Customer support fund, bill credit100
Expanded credit for limited income customers300
Customer assistance, small customers, bill credit1,000
Additional bill credit for delinquent limited income customers250
Customer support fund, non-profits and community organizations $ 2,700,000
Damage from Fire, Explosion or Other Hazard
Public Utilities, General Disclosures [Line Items]
Customer support fund, payment period8 months
Past due balance threshold qualifying for payment extension $ 75

Regulatory Matters - Retail Rat

Regulatory Matters - Retail Rate Case Filing (Details)Nov. 06, 2020USD ($)Oct. 31, 2019USD ($)$ / kWhGWJun. 30, 2019USD ($)Aug. 13, 2018USD ($)Jan. 08, 2018USD ($)Mar. 27, 2017USD ($)$ / kWhDec. 31, 2020USD ($)Dec. 04, 2020USD ($)Oct. 02, 2020USD ($)
ACC
Public Utilities, General Disclosures [Line Items]
Revenue increase (decrease) $ 169,000,000 $ 59,800,000 $ 89,700,000
Average annual customer bill increase (decrease), percent5.14%1.82%2.70%
Recommended return on equity, percentage10.00%9.40%
Alternative, percentage0.30%
Increment of fair value rate, percentage0.80%0.00%
Residential Utility Consumer Office
Public Utilities, General Disclosures [Line Items]
Revenue increase (decrease) $ (50,100,000) $ (20,800,000)
Average annual customer bill increase (decrease), percent(1.52%)(0.63%)
Recommended return on equity, percentage8.74%
Increment of fair value rate, percentage0.00%
ACC | APS
Public Utilities, General Disclosures [Line Items]
Proposed annual revenue increase $ 184,000,000 $ (86,500,000) $ (119,100,000)
Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS
Public Utilities, General Disclosures [Line Items]
Base rate decrease, elimination of tax expense adjustment mechanism $ 115,000,000
Approximate percentage of increase in average customer bill5.60%3.28%
Approximate percentage of increase in average residential customer bill5.40%4.54%
Rate matter, cost base rate $ 8,870,000,000
Base fuel rate (in dollars per kWh) | $ / kWh0.030168
Funding limited income crisis bill program $ 1,250,000
Commercial customers, market pricing, threshold | GW0.02
Net retail base rate, increase $ 94,600,000
Non-fuel and non-depreciation base rate, increase87,200,000
Fuel-related base rate decrease53,600,000
Base rate increase, changes in depreciation schedules $ 61,000,000
Authorized return on common equity (as a percent)10.00%
Percentage of debt in capital structure44.20%
Percentage of common equity in capital structure55.80%
Rate matter, resource comparison proxy for exported energy (in dollars per kWh) | $ / kWh0.129
AZ Sun Program Phase 2 | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS
Public Utilities, General Disclosures [Line Items]
Public utilities, minimum annual renewable energy standard and tariff $ 10,000,000
Public utilities, maximum annual renewable energy standard and tariff $ 15,000,000
Coal Community Transition Plan | ACC
Public Utilities, General Disclosures [Line Items]
Amount funded by shareholders $ 25,000,000 $ 25,000,000
Amount funded by customers, term10 years
Amount funded by customers $ 100,000,000
Coal Community Transition Plan | ACC | Navajo Nation, Economic Development Organization
Public Utilities, General Disclosures [Line Items]
Amount funded by shareholders $ 1,250,000
Amount funded by shareholders, term5 years
Coal Community Transition Plan | ACC | Navajo Nation, Electrification Projects
Public Utilities, General Disclosures [Line Items]
Amount funded by shareholders $ 10,000,000
Amount funded by customers10,000,000
Coal Community Transition Plan | ACC | Navajo Nation, Transmission Revenue Sharing
Public Utilities, General Disclosures [Line Items]
Amount funded by shareholders $ 2,500,000
Coal Community Transition Plan | ACC | Navajo County Communities, Cholla Power Plant Closure
Public Utilities, General Disclosures [Line Items]
Amount funded by customers, term5 years
Amount funded by customers $ 12,000,000
Coal Community Transition Plan | ACC | Navajo Nation, Generation Station
Public Utilities, General Disclosures [Line Items]
Amount funded by customers $ 3,700,000
Minimum | ACC | APS
Public Utilities, General Disclosures [Line Items]
Annual increase in retail base rates $ 69,000,000
Minimum | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS
Public Utilities, General Disclosures [Line Items]
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh0.00016
Maximum | Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS
Public Utilities, General Disclosures [Line Items]
Rate matter, environmental surcharge cap rate (in dollars per kWh) | $ / kWh0.00050

Regulatory Matters - Capital St

Regulatory Matters - Capital Structure and Costs of Capital (Details) - $ / kWhOct. 01, 2021May 01, 2020Oct. 31, 2019May 01, 2019
Cost of Capital
Long-term debt4.10%
Common stock equity10.15%
Weighted-average cost of capital7.41%
Retail Rate Case Filing with Arizona Corporation Commission | APS
Capital Structure
Common stock equity54.70%
Retail Rate Case Filing with Arizona Corporation Commission | ACC | APS
Capital Structure
Long-term debt45.30%
Net Metering | ACC | APS
Cost of Capital
Second-year export energy price (in dollars per kWh)0.094 0.105
Net Metering | ACC | APS | Forecast
Cost of Capital
Second-year export energy price (in dollars per kWh)0.105

Regulatory Matters - Cost Recov

Regulatory Matters - Cost Recovery Mechanisms (Details)Oct. 01, 2021$ / kWhFeb. 22, 2021USD ($)Feb. 15, 2021USD ($)Feb. 01, 2021USD ($)$ / kWhAug. 20, 2020USD ($)CustomerJun. 01, 2020USD ($)May 01, 2020$ / kWhFeb. 14, 2020USD ($)Feb. 01, 2020$ / kWhNov. 14, 2019USD ($)CustomerOct. 31, 2019USD ($)Oct. 29, 2019USD ($)Jun. 01, 2019USD ($)May 01, 2019$ / kWhApr. 10, 2019Feb. 15, 2019USD ($)Feb. 01, 2019$ / kWhAug. 13, 2018USD ($)Feb. 15, 2018USD ($)Feb. 01, 2018$ / kWhJan. 08, 2018USD ($)Nov. 20, 2017USD ($)Sep. 01, 2017USD ($)$ / kWhMar. 31, 2021USD ($)$ / kWhMar. 31, 2021USD ($)Mar. 31, 2020USD ($)Dec. 31, 2020USD ($)programMWDec. 31, 2017$ / kWhJul. 01, 2020USD ($)May 15, 2020USD ($)May 05, 2020USD ($)Dec. 31, 2019USD ($)Jul. 01, 2019USD ($)Mar. 15, 2019agreementDec. 31, 2018USD ($)Jun. 29, 2018USD ($)Nov. 14, 2017USD ($)
Change in regulatory asset
Deferred fuel and purchased power costs — current period $ 52,210,000 $ 5,785,000
Amounts refunded to customers564,000 1,808,000
Rate plan comparison tool, number of customers | Customer3,800 13,000
Rate plan comparison tool, inconvenience payment $ 25 $ 25
APS
Change in regulatory asset
Deferred fuel and purchased power costs — current period52,210,000 5,785,000
Amounts refunded to customers564,000 1,808,000
Percentage increase under PSA effective for first billing cycle beginning April 202150.00%
Remaining percentage increase under PSA effective for first billing cycle beginning November 202150.00%
Demand side management funds $ 36,000,000
Customer credits $ 43,000,000 43,000,000
Customer credits, additional funds $ 7,000,000 $ 7,000,000
APS | 2017 Settlement Agreement and its Customer Education and Outreach Plan
Change in regulatory asset
Settlement amount $ 24,750,000
Settlement amount returned to customers $ 24,000,000
Lost Fixed Cost Recovery Mechanisms | APS
Change in regulatory asset
Fixed cost recoverable per power lost (in dollars per kWh) | $ / kWh0.025
Percentage of retail revenues1.00%1.00%
Amount of adjustment representing prorated sales losses pending approval $ 38,500,000 $ 26,600,000 $ 36,200,000 $ 60,700,000
Increase (decrease) in amount of adjustment representing prorated sales losses $ 11,800,000 $ (9,600,000) $ (24,500,000)
ACC | APS
Settlement Agreement
Program term18 years
Change in regulatory asset
Gross-up for revenue requirement of rate regulation $ (184,000,000) $ 86,500,000 $ 119,100,000
Deferred taxes amortization, period28 years 6 months
Public Utilities, one-time bill credit $ 64,000,000
Public Utilities, one-time bill credit, additional benefit $ 39,500,000
Number of programs | program2
Solar power capacity (in MW) | MW80
ACC | RES | APS
Settlement Agreement
Plan term5 years
ACC | RES 2018 | APS
Settlement Agreement
Amount of proposed budget $ 84,700,000 $ 86,300,000 $ 89,900,000
Revenue requirements $ 4,500,000
ACC | RES 2018 | APS | Solar Communities
Settlement Agreement
Program term3 years
ACC | Demand Side Management Adjustor Charge 2018 | APS
Settlement Agreement
Amount of proposed budget $ 52,600,000 $ 52,600,000
ACC | Demand Side Management Adjustor Charge 2019 | APS
Settlement Agreement
Amount of proposed budget $ 34,100,000
ACC | Demand Side Management Adjustor Charge 2020 | APS
Settlement Agreement
Amount of proposed budget $ 51,900,000 $ 51,900,000
ACC | Power Supply Adjustor (PSA) | APS
Change in regulatory asset
Beginning balance $ 175,835,000 70,137,000 $ 70,137,000
Deferred fuel and purchased power costs — current period52,210,000 5,785,000
Amounts refunded to customers564,000 1,808,000
Ending balance $ 228,609,000 $ 228,609,000 $ 77,730,000 175,835,000
PSA rate (in dollars per kWh) | $ / kWh0.003544 (0.000456)0.001658 0.004555 0.001544
PSA rate for prior year (in dollars per kWh) | $ / kWh0.003434 (0.002086)0.000536 (0.004444)
Forward component of increase in PSA (in dollars per kWh) | $ / kWh0.000110 0.001630 0.001122 0.005988
ACC | Net Metering | APS
Change in regulatory asset
Cost of service, resource comparison proxy method, maximum annual percentage decrease10.00%
Cost of service for interconnected DG system customers, grandfathered period20 years
Cost of service for new customers, guaranteed export price period10 years
First-year export energy price (in dollars per kWh) | $ / kWh0.129
Second-year export energy price (in dollars per kWh) | $ / kWh0.094 0.105
ACC | Demand Side Management Adjustor Charge 2021 | APS
Settlement Agreement
Amount of proposed budget $ 63,700,000
United States Federal Energy Regulatory Commission | Environmental Improvement Surcharge | APS
Change in regulatory asset
Increase (decrease) in annual wholesale transmission rates $ 10,300,000
Rate matters, increase (decrease) in cost recovery, excess of annual amount $ 1,500,000
United States Federal Energy Regulatory Commission | Open Access Transmission Tariff | APS
Change in regulatory asset
Increase (decrease) in annual wholesale transmission rates $ (6,100,000) $ 25,800,000
Retail customer rates $ 10,900,000 $ 4,700,000
Cost Recovery Mechanisms | ACC | Power Supply Adjustor (PSA) | APS
Change in regulatory asset
Historical component of increase in PSA (in dollars per kWh) | $ / kWh0.004 (0.002115)(0.002897)
Cost recovery, number of agreements | agreement2
Forecast | ACC | Net Metering | APS
Change in regulatory asset
Second-year export energy price (in dollars per kWh) | $ / kWh0.105
Minimum | ACC | APS
Change in regulatory asset
Operating results $ (69,000,000)
Minimum | ACC | RES 2018 | APS | Solar Communities
Settlement Agreement
Required annual capital investment $ 10,000,000
Maximum | ACC | RES 2018 | APS | Solar Communities
Settlement Agreement
Required annual capital investment $ 15,000,000

Regulatory Matters - Four Corne

Regulatory Matters - Four Corners and Cholla (Details) - APS - USD ($) $ in Millions1 Months Ended
Sep. 30, 2018Apr. 30, 2018Mar. 31, 2021
SCE | Four Corners Units 4 and 5
Business Acquisition [Line Items]
Settlement agreement, ACC approved rate adjustment, annualized customer impact $ 58.5 $ 67.5
Retired power plant costs
Business Acquisition [Line Items]
Net book value $ 52.9
Navajo Plant
Business Acquisition [Line Items]
Net book value69.4
Navajo Plant, Coal Reclamation Regulatory Asset
Business Acquisition [Line Items]
Net book value $ 17.8

Regulatory Matters - Schedule o

Regulatory Matters - Schedule of Regulatory Assets (Details) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Detail of regulatory assets
Current $ 339,880 $ 291,713
Non-Current1,135,857 1,133,987
Pension
Detail of regulatory assets
Current0 0
Non-Current467,423 469,953
Deferred fuel and purchased power
Detail of regulatory assets
Current228,609 175,835
Non-Current0 0
Income taxes — allowance for funds used during construction (“AFUDC”) equity
Detail of regulatory assets
Current7,169 7,169
Non-Current159,119 158,776
Retired power plant costs
Detail of regulatory assets
Current28,182 28,181
Non-Current107,169 114,214
Ocotillo deferral
Detail of regulatory assets
Current0 0
Non-Current110,820 95,723
SCR deferral
Detail of regulatory assets
Current0 0
Non-Current88,044 81,307
Deferred property taxes
Detail of regulatory assets
Current8,569 8,569
Non-Current47,484 49,626
Lost fixed cost recovery
Detail of regulatory assets
Current45,905 41,807
Non-Current0 0
Deferred compensation
Detail of regulatory assets
Current0 0
Non-Current35,806 36,195
Four Corners cost deferral
Detail of regulatory assets
Current8,077 8,077
Non-Current22,056 24,075
Income taxes — investment tax credit basis adjustment
Detail of regulatory assets
Current1,113 1,113
Non-Current24,221 24,291
Palo Verde VIEs (Note 6)
Detail of regulatory assets
Current0 0
Non-Current21,409 21,255
Coal reclamation
Detail of regulatory assets
Current1,068 1,068
Non-Current16,732 16,999
Loss on reacquired debt
Detail of regulatory assets
Current1,703 1,689
Non-Current10,486 10,877
Mead-Phoenix transmission line contributions in aid of construction (“CIAC”)
Detail of regulatory assets
Current332 332
Non-Current9,297 9,380
Demand side management
Detail of regulatory assets
Current0 0
Non-Current7,268 7,268
Tax expense adjustor mechanism
Detail of regulatory assets
Current5,854 6,226
Non-Current0 0
Tax expense of Medicare subsidy
Detail of regulatory assets
Current1,235 1,235
Non-Current3,626 3,704
Deferred fuel and purchased power — mark-to-market (Note 7)
Detail of regulatory assets
Current0 3,341
Non-Current3,728 9,244
PSA Interest
Detail of regulatory assets
Current46 4,355
Non-Current0 0
Other
Detail of regulatory assets
Current2,018 2,716
Non-Current $ 1,169 $ 1,100

Regulatory Matters - Schedule_2

Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in ThousandsDec. 31, 2022Mar. 31, 2021Dec. 31, 2020
Detail of regulatory liabilities
Current $ 250,228 $ 229,088
Non-Current2,427,769 2,450,169
Asset retirement obligations
Detail of regulatory liabilities
Current0 0
Non-Current519,015 506,049
Other postretirement benefits
Detail of regulatory liabilities
Current37,705 37,705
Non-Current337,853 349,588
Removal costs
Detail of regulatory liabilities
Current55,247 52,844
Non-Current89,937 103,008
Income taxes — change in rates
Detail of regulatory liabilities
Current2,839 2,839
Non-Current66,374 66,553
Four Corners coal reclamation
Detail of regulatory liabilities
Current5,461 5,460
Non-Current49,703 49,435
Income taxes — deferred investment tax credit
Detail of regulatory liabilities
Current2,231 2,231
Non-Current48,507 48,648
Spent nuclear fuel
Detail of regulatory liabilities
Current6,831 6,768
Non-Current43,059 44,221
Renewable energy standard
Detail of regulatory liabilities
Current34,460 39,442
Non-Current30 103
Deferred fuel and purchased power — mark-to-market (Note 7)
Detail of regulatory liabilities
Current20,829 0
Non-Current0 0
Property tax deferral
Detail of regulatory liabilities
Current0 0
Non-Current15,022 13,856
Sundance maintenance
Detail of regulatory liabilities
Current2,867 2,989
Non-Current11,910 11,508
Demand side management
Detail of regulatory liabilities
Current7,821 10,819
Non-Current5,975 0
FERC transmission true up
Detail of regulatory liabilities
Current7,630 6,598
Non-Current2,379 3,008
TCA balancing account
Detail of regulatory liabilities
Current7,315 2,902
Non-Current1,754 4,672
Tax expense adjustor mechanism
Detail of regulatory liabilities
Current7,452 7,089
Non-Current0 0
Tax expense adjustor mechanism | Forecast
Detail of regulatory liabilities
Current $ 7,000
Deferred gains on utility property
Detail of regulatory liabilities
Current2,423 2,423
Non-Current939 1,544
Active union medical trust
Detail of regulatory liabilities
Current0 0
Non-Current2,337 6,057
Other
Detail of regulatory liabilities
Current524 409
Non-Current59 189
ACC | Excess deferred income taxes - ACC - Tax Cuts and Jobs Act
Detail of regulatory liabilities
Current41,353 41,330
Non-Current1,004,226 1,012,583
United States Federal Energy Regulatory Commission | Excess deferred income taxes - ACC - Tax Cuts and Jobs Act
Detail of regulatory liabilities
Current7,240 7,240
Non-Current $ 228,690 $ 229,147

Retirement Plans and Other Po_3

Retirement Plans and Other Postretirement Benefits - Narrative (Details) - USD ($)Jan. 04, 2021Mar. 31, 2021Dec. 31, 2020Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial pre-65 ultimate health care cost trend rate (as a percent)4.75%
Initial post-65 healthcare cost trend rate (as a percent)2.00%
Transfer to active union medical account $ (106,000,000)
Contributions
Expected voluntary employer contributions in the next fiscal year $ 0
Expected voluntary employer contributions in the year after next fiscal year0
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Transfer to active union medical account106,000,000
Contributions
Estimated future employer contributions in next three years0
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Transfer to active union medical account $ (106,000,000)
Contributions
Voluntary contributions0
Minimum employer contributions for the next three years0
Expected voluntary employer contributions in the remainder of the current fiscal year $ 100,000,000

Retirement Plans and Other Po_4

Retirement Plans and Other Postretirement Benefits - Schedule of Net Benefit Cost (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Amortization of:
Portion of cost/(benefit) charged to expense $ (27,791) $ (13,911)
Pension Benefits
Retirement Plans and Other Benefits
Service cost — benefits earned during the period15,679 14,257
Interest cost on benefit obligation24,669 29,761
Expected return on plan assets(50,608)(46,806)
Amortization of:
Prior service credit0 0
Net actuarial loss (gain)3,985 9,011
Net periodic benefit cost/(benefit)(6,275)6,223
Portion of cost/(benefit) charged to expense(8,011)1,342
Other Benefits
Retirement Plans and Other Benefits
Service cost — benefits earned during the period4,557 5,717
Interest cost on benefit obligation4,162 6,512
Expected return on plan assets(10,361)(10,019)
Amortization of:
Prior service credit(9,427)(9,394)
Net actuarial loss (gain)(2,405)0
Net periodic benefit cost/(benefit)(13,474)(7,184)
Portion of cost/(benefit) charged to expense $ (9,528) $ (5,456)

Palo Verde Sale Leaseback Var_3

Palo Verde Sale Leaseback Variable Interest Entities - Narrative (Details)3 Months Ended
Mar. 31, 2021USD ($)Leasepower_plantMar. 31, 2020USD ($)Dec. 31, 1986Trust
Palo Verde Sale Leaseback Variable Interest Entities
Net income attributable to noncontrolling interests $ 4,873,000 $ 4,873,000
APS
Palo Verde Sale Leaseback Variable Interest Entities
Number of VIE lessor trusts3 3
Net income attributable to noncontrolling interests $ 4,873,000 4,873,000
Palo Verde VIE | APS
Palo Verde Sale Leaseback Variable Interest Entities
Net income attributable to noncontrolling interests5,000,000 $ 5,000,000
Initial loss exposure to the VIE's noncontrolling equity participants during lease extension period307,000,000
Maximum loss exposure to the VIE's noncontrolling equity participants during lease extension period $ 501,000,000
Palo Verde VIE | APS | Period through 2023
Palo Verde Sale Leaseback Variable Interest Entities
Number of leases under which assets are retained | Lease1
Palo Verde VIE | APS | Period through 2033
Palo Verde Sale Leaseback Variable Interest Entities
Number of leases under which assets are retained | Lease2
Palo Verde VIE | APS | Period 2021 through 2033
Palo Verde Sale Leaseback Variable Interest Entities
Number of leases under which assets are retained | Lease3
Annual lease payments $ 21,000,000
Palo Verde VIE | APS | Period 2021 through 2033 | Maximum
Palo Verde Sale Leaseback Variable Interest Entities
Lease period (up to)2 years

Palo Verde Sale Leaseback Var_4

Palo Verde Sale Leaseback Variable Interest Entities - Schedule of VIEs (Details) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Palo Verde Sale Leaseback Variable Interest Entities
Palo Verde sale leaseback property, plant and equipment, net of accumulated depreciation $ 15,315,701 $ 15,159,210
Amounts relating to the VIEs included in Condensed Consolidated Balance Sheets
Equity — Noncontrolling interests124,164 119,290
APS
Palo Verde Sale Leaseback Variable Interest Entities
Palo Verde sale leaseback property, plant and equipment, net of accumulated depreciation15,315,340 15,158,846
Amounts relating to the VIEs included in Condensed Consolidated Balance Sheets
Equity — Noncontrolling interests124,164 119,290
Palo Verde VIE | APS
Palo Verde Sale Leaseback Variable Interest Entities
Palo Verde sale leaseback property, plant and equipment, net of accumulated depreciation97,068 98,036
Amounts relating to the VIEs included in Condensed Consolidated Balance Sheets
Equity — Noncontrolling interests $ 124,164 $ 119,290

Derivative Accounting - Narrati

Derivative Accounting - Narrative (Details) - USD ($)Mar. 31, 2021Mar. 31, 2021Mar. 31, 2020
Derivative Accounting
Amounts reclassified from accumulated other comprehensive income in next twelve months $ 0
Commodity Contracts
Derivative Accounting
Aggregate fair value of derivative instruments in a net liability position $ 11,520,000 11,520,000
Additional collateral to counterparties for energy related non-derivative instrument contracts $ 86,000,000 86,000,000
Commodity Contracts | Designated as Hedging Instruments
Derivative Accounting
Amount reclassified from accumulated other comprehensive income to earnings related to discontinued cash flow hedges $ 0 $ 0
APS
Derivative Accounting
Percentage of unrealized gains and losses on certain derivatives deferred for future rate treatment100.00%100.00%
Risk Management Assets | Credit Concentration Risk
Derivative Accounting
Concentration risk59.00%
Aggregate fair value of derivative instruments in a net liability position $ 26,000,000 $ 26,000,000

Derivative Accounting - Schedul

Derivative Accounting - Schedule of Gross Notional Amounts Outstanding (Details) - Commodity Contracts GWh in Thousands, Bcf in ThousandsMar. 31, 2021GWhBcfDec. 31, 2020GWhBcf
Outstanding gross notional amount of derivatives
Power | GWh368 368
Gas | Bcf211 205

Derivative Accounting - Gains a

Derivative Accounting - Gains and Losses from Derivative Instruments (Details) - Commodity Contracts - USD ($)3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Designated as Hedging Instruments
Gains and losses from derivative instruments
Amount reclassified from accumulated other comprehensive income to earnings related to discontinued cash flow hedges $ 0 $ 0
Designated as Hedging Instruments | Fuel and purchased power
Gains and losses from derivative instruments
Loss Reclassified from Accumulated OCI into Income (Effective Portion Realized)0 (414,000)
Not Designated as Hedging Instruments | Fuel and purchased power
Gains and losses from derivative instruments
Net Gain (Loss) Recognized in Income $ 26,859,000 $ (30,078,000)

Derivative Accounting - Derivat

Derivative Accounting - Derivative Instruments in the Balance Sheets (Details) - USD ($)Mar. 31, 2021Dec. 31, 2020
Assets
Gross Recognized Derivatives $ 25,811,000 $ 4,749,000
Liabilities
Amount Reported on Balance Sheet(9,995,000)(18,619,000)
Commodity Contracts
Assets
Gross Recognized Derivatives29,693,000 9,020,000
Amounts Offset(3,882,000)(4,271,000)
Net Recognized Derivatives25,811,000 4,749,000
Other0 0
Amount Reported on Balance Sheet25,811,000 4,749,000
Liabilities
Gross Recognized Derivatives(12,592,000)(21,605,000)
Amounts Offset3,882,000 4,271,000
Net Recognized Derivatives(8,710,000)(17,334,000)
Other(1,285,000)(1,285,000)
Amount Reported on Balance Sheet(9,995,000)(18,619,000)
Assets and Liabilities
Gross Recognized Derivatives17,101,000 (12,585,000)
Amounts Offset0 0
Net Recognized Derivatives17,101,000 (12,585,000)
Other(1,285,000)(1,285,000)
Amount Reported on Balance Sheet15,816,000 (13,870,000)
Cash collateral received from counterparties1,285,000 1,285,000
Commodity Contracts | Current assets
Assets
Gross Recognized Derivatives25,703,000 5,870,000
Amounts Offset(3,092,000)(2,939,000)
Net Recognized Derivatives22,611,000 2,931,000
Other0 0
Amount Reported on Balance Sheet22,611,000 2,931,000
Commodity Contracts | Investments and other assets
Assets
Gross Recognized Derivatives3,990,000 3,150,000
Amounts Offset(790,000)(1,332,000)
Net Recognized Derivatives3,200,000 1,818,000
Other0 0
Amount Reported on Balance Sheet3,200,000 1,818,000
Commodity Contracts | Current liabilities
Liabilities
Gross Recognized Derivatives(4,874,000)(9,211,000)
Amounts Offset3,092,000 2,939,000
Net Recognized Derivatives(1,782,000)(6,272,000)
Other(1,285,000)(1,285,000)
Amount Reported on Balance Sheet(3,067,000)(7,557,000)
Assets and Liabilities
Cash collateral received from counterparties1,285,000 1,285,000
Commodity Contracts | Deferred credits and other
Liabilities
Gross Recognized Derivatives(7,718,000)(12,394,000)
Amounts Offset790,000 1,332,000
Net Recognized Derivatives(6,928,000)(11,062,000)
Other0 0
Amount Reported on Balance Sheet(6,928,000)(11,062,000)
Assets and Liabilities
Cash collateral received from counterparties $ 0 $ 0

Derivative Accounting - Credit

Derivative Accounting - Credit Risk and Credit Related Contingent Features (Details) - Commodity Contracts $ in ThousandsMar. 31, 2021USD ($)
Credit Risk and Credit-Related Contingent Features
Aggregate fair value of derivative instruments in a net liability position $ 11,520
Cash collateral posted0
Additional cash collateral in the event credit-risk-related contingent features were fully triggered $ 6,674

Commitments and Contingencies -

Commitments and Contingencies - Palo Verde Nuclear Generating Station and Contractual Obligations (Details)Mar. 15, 2021USD ($)Nov. 02, 2020claimOct. 31, 2019USD ($)Mar. 31, 2021USD ($)power_plantJun. 30, 2018USD ($)claimtime_periodDec. 31, 1986Trust
Breach of Contract for Disposal of Spent Nuclear Fuel and/or High Level Radioactive Waste
Commitments and Contingencies
Litigation settlement amount $ 12,100,000 $ 12,200,000 $ 99,700,000
APS
Commitments and Contingencies
Maximum insurance against public liability per occurrence for a nuclear incident (up to) $ 13,700,000,000
Maximum available nuclear liability insurance (up to)450,000,000
Remaining nuclear liability insurance through mandatory industry wide retrospective assessment program13,200,000,000
Maximum retrospective premium assessment per reactor for each nuclear liability incident137,600,000
Annual limit per incident with respect to maximum retrospective premium assessment $ 20,500,000
Number of VIE lessor trusts3 3
Maximum potential retrospective assessment per incident of APS $ 120,100,000
Annual payment limitation with respect to maximum potential retrospective premium assessment17,900,000
Amount of "all risk" (including nuclear hazards) insurance for property damage to, and decontamination of, property at Palo Verde2,800,000,000
Maximum amount that APS could incur under the current NEIL policies for each retrospective assessment22,400,000
Collateral assurance provided based on rating triggers $ 63,300,000
Period to provide collateral assurance based on rating triggers20 days
APS | Public Utilities, Inventory, Fuel
Commitments and Contingencies
Purchase obligation $ 550,000,000
APS | Breach of Contract for Disposal of Spent Nuclear Fuel and/or High Level Radioactive Waste
Commitments and Contingencies
Litigation settlement amount $ 3,500,000 $ 3,600,000 $ 29,000,000
Number of claims submitted | claim7 6
Number of settlement agreement time periods | time_period6

Commitments and Contingencies_2

Commitments and Contingencies - Superfund-Related Matters, Southwest Power Outage and Clean Air Act (Details) - APS - Contaminated groundwater wells $ in MillionsApr. 05, 2018DefendantplaintiffDec. 16, 2016plaintiffAug. 06, 2013DefendantMar. 31, 2021USD ($)
Loss Contingencies [Line Items]
Costs related to investigation and study under Superfund site | $ $ 3
Number of defendants against whom Roosevelt Irrigation District (RID) filed lawsuit | Defendant28 24
Number of plaintiffs2
Settled Litigation
Loss Contingencies [Line Items]
Number of plaintiffs2

Commitments and Contingencies_3

Commitments and Contingencies - Environmental Matters and Financial Assurances (Details) - USD ($) $ in ThousandsFeb. 22, 2021Jul. 03, 2018Jul. 06, 2016Mar. 31, 2021
Financial Assurances
Production tax credit guarantees $ 2,000
Equity contribution guarantees38,000
APS | 2017 Settlement Agreement and its Customer Education and Outreach Plan
Arizona Attorney General [Abstract]
Settlement amount $ 24,750
Settlement amount returned to customers $ 24,000
APS | Letters of Credit Expiring in 2020
Financial Assurances
Outstanding letters of credit5,200
APS | Surety Bonds Expiring in 2020
Financial Assurances
Surety bonds expiring, amount16,000
4C Acquisition, LLC | Four Corners
Environmental Matters [Abstract]
Percentage of share of cost of control7.00%
Four Corners Coal Supply Agreement
Notes receivable, related parties23,000
4C Acquisition, LLC | Coal Supply Agreement Arbitration | Four Corners
Four Corners Coal Supply Agreement
Reimbursement payments due to 4CA $ 10,000
NTEC | Four Corners
Four Corners Coal Supply Agreement
Option to purchase ownership interest (as a percent)7.00%7.00%
Proceeds from operating and maintenance cost reimbursement $ 70,000
NTEC | Coal Supply Agreement Arbitration | Four Corners
Four Corners Coal Supply Agreement
Option to purchase ownership interest (as a percent)7.00%
Regional Haze Rules | APS | Four Corners Units 4 and 5
Environmental Matters [Abstract]
Percentage of share of cost of control63.00%
Expected environmental cost $ 400,000
Regional Haze Rules | APS | Natural gas tolling contract obligations | Four Corners Units 4 and 5
Environmental Matters [Abstract]
Additional percentage share of cost of control7.00%
Regional Haze Rules | APS | Four Corners | Four Corners Units 4 and 5
Environmental Matters [Abstract]
Site contingency increase in loss exposure not accrued, best estimate $ 45,000
Coal combustion waste | APS | Four Corners
Environmental Matters [Abstract]
Site contingency increase in loss exposure not accrued, best estimate27,000
Coal combustion waste | APS | Navajo Plant
Environmental Matters [Abstract]
Site contingency increase in loss exposure not accrued, best estimate1,000
Minimum | Coal combustion waste | APS | Cholla
Environmental Matters [Abstract]
Site contingency increase in loss exposure not accrued, best estimate16,000
Minimum | Coal combustion waste | APS | Cholla and Four Corners
Environmental Matters [Abstract]
Site contingency increase in loss exposure not accrued, best estimate10,000
Maximum | Coal combustion waste | APS | Cholla and Four Corners
Environmental Matters [Abstract]
Site contingency increase in loss exposure not accrued, best estimate $ 15,000

Other Income and Other Expens_2

Other Income and Other Expense (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Other income:
Interest income $ 1,948 $ 3,277
Miscellaneous3 8
Total other income12,429 12,569
Other expense:
Non-operating costs(1,937)(2,658)
Investment gains (losses) — net(343)60
Miscellaneous(1,573)(2,186)
Total other expense(3,853)(4,784)
APS
Other income:
Interest income1,481 2,341
Miscellaneous1 8
Total other income11,960 11,633
Other expense:
Non-operating costs(1,778)(2,482)
Miscellaneous(1,572)(2,186)
Total other expense(3,350)(4,668)
SCR deferral
Other income:
Debt return on Four Corners SCR deferrals (Note 4)4,086 3,140
SCR deferral | APS
Other income:
Debt return on Four Corners SCR deferrals (Note 4)4,086 3,140
Ocotillo deferral
Other income:
Debt return on Four Corners SCR deferrals (Note 4)6,392 6,144
Ocotillo deferral | APS
Other income:
Debt return on Four Corners SCR deferrals (Note 4) $ 6,392 $ 6,144

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
Earnings Per Share [Abstract]
Net income attributable to common shareholders $ 35,641 $ 29,993
Weighted average common shares outstanding - basic (in shares)112,829 112,594
Net effect of dilutive securities:
Contingently issuable performance shares and restricted stock units (in shares)264 268
Weighted average common shares outstanding — diluted (in shares)113,093 112,862
Earnings per weighted-average common share outstanding
Net income attributable to common shareholders - basic (in dollars per share) $ 0.32 $ 0.27
Net income attributable to common shareholders - diluted (in dollars per share) $ 0.32 $ 0.27

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in ThousandsMar. 31, 2021Dec. 31, 2020
Assets
Commodity contracts, assets $ 25,811 $ 4,749
Commodity contracts, liabilities(3,882)(4,271)
Nuclear decommissioning trust1,159,699 1,138,435
Nuclear decommissioning trust, other632,661 592,227
Other special use funds357,506 254,509
Other special use funds, other1,401 504
Total assets1,543,016 1,397,693
Total assets, other630,180 588,460
Liabilities
Gross derivative liability, other2,597 2,986
Amount reported on balance sheet(9,995)(18,619)
Equity securities
Assets
Nuclear decommissioning trust6,622 11,968
Nuclear decommissioning trust, other(15,538)(17,828)
Other special use funds20,612 37,841
Other special use funds, other1,401 504
U.S. commingled equity funds
Assets
Nuclear decommissioning trust648,199 610,055
U.S. Treasury debt
Assets
Nuclear decommissioning trust175,707 164,514
Other special use funds323,589 203,220
Corporate debt
Assets
Nuclear decommissioning trust143,876 149,509
Mortgage-backed securities
Assets
Nuclear decommissioning trust110,073 99,623
Municipal bonds
Assets
Nuclear decommissioning trust64,479 89,705
Other special use funds13,305 13,448
Other fixed income
Assets
Nuclear decommissioning trust10,743 13,061
Level 1
Assets
Commodity contracts, assets0 0
Nuclear decommissioning trust197,867 194,310
Other special use funds342,800 240,557
Total assets540,667 434,867
Liabilities
Gross derivative liability0 0
Level 1 | Equity securities
Assets
Nuclear decommissioning trust22,160 29,796
Other special use funds19,211 37,337
Level 1 | U.S. commingled equity funds
Assets
Nuclear decommissioning trust0 0
Level 1 | U.S. Treasury debt
Assets
Nuclear decommissioning trust175,707 164,514
Other special use funds323,589 203,220
Level 1 | Corporate debt
Assets
Nuclear decommissioning trust0 0
Level 1 | Mortgage-backed securities
Assets
Nuclear decommissioning trust0 0
Level 1 | Municipal bonds
Assets
Nuclear decommissioning trust0 0
Other special use funds0 0
Level 1 | Other fixed income
Assets
Nuclear decommissioning trust0 0
Level 2
Assets
Commodity contracts, assets14,353 9,016
Nuclear decommissioning trust329,171 351,898
Other special use funds13,305 13,448
Total assets356,829 374,362
Liabilities
Gross derivative liability(11,668)(20,498)
Level 2 | Equity securities
Assets
Nuclear decommissioning trust0 0
Other special use funds0 0
Level 2 | U.S. commingled equity funds
Assets
Nuclear decommissioning trust0 0
Level 2 | U.S. Treasury debt
Assets
Nuclear decommissioning trust0 0
Other special use funds0 0
Level 2 | Corporate debt
Assets
Nuclear decommissioning trust143,876 149,509
Level 2 | Mortgage-backed securities
Assets
Nuclear decommissioning trust110,073 99,623
Level 2 | Municipal bonds
Assets
Nuclear decommissioning trust64,479 89,705
Other special use funds13,305 13,448
Level 2 | Other fixed income
Assets
Nuclear decommissioning trust10,743 13,061
Level 3
Assets
Commodity contracts, assets15,340 4
Nuclear decommissioning trust0 0
Other special use funds0 0
Total assets15,340 4
Liabilities
Gross derivative liability(924)(1,107)
Level 3 | Equity securities
Assets
Nuclear decommissioning trust0 0
Other special use funds0 0
Level 3 | U.S. commingled equity funds
Assets
Nuclear decommissioning trust0 0
Level 3 | U.S. Treasury debt
Assets
Nuclear decommissioning trust0 0
Other special use funds0 0
Level 3 | Corporate debt
Assets
Nuclear decommissioning trust0 0
Level 3 | Mortgage-backed securities
Assets
Nuclear decommissioning trust0 0
Level 3 | Municipal bonds
Assets
Nuclear decommissioning trust0 0
Other special use funds0 0
Level 3 | Other fixed income
Assets
Nuclear decommissioning trust0 0
Fair Value Measured at Net Asset Value Per Share | U.S. commingled equity funds
Assets
Nuclear decommissioning trust $ 648,199 $ 610,055

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in MillionsMar. 31, 2021Dec. 31, 2020
Fair Value Disclosures [Abstract]
Stated interest rate for notes receivable3.90%
Note receivable, net book value $ 22.7 $ 27.1

Investments in Nuclear Decomm_3

Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - USD ($) $ in ThousandsJan. 04, 2021Mar. 31, 2021Mar. 31, 2020Dec. 31, 2020Dec. 31, 2019
Fair value of fixed income securities, summarized by contractual maturities
Transfer to active union medical account $ 106,000
APS
Nuclear decommissioning trust fund assets
Fair Value $ 1,517,205 $ 1,392,944
Total Unrealized Gains484,780 468,247
Total Unrealized Losses(3,203)(398)
Amortized cost818,000 687,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains2,968 $ 3,313
Realized losses(4,148)(2,227)
Proceeds from the sale of securities379,978 195,087
Fair value of fixed income securities, summarized by contractual maturities
Employee medical claims amount14,000 $ 15,000
APS | Equity securities
Nuclear decommissioning trust fund assets
Equity securities689,570 677,188
Total Unrealized Gains457,442 421,666
Total Unrealized Losses0 0
APS | Available for sale-fixed income securities
Nuclear decommissioning trust fund assets
Fair Value841,772 733,080
Total Unrealized Gains27,338 46,581
Total Unrealized Losses(3,203)(398)
Fair value of fixed income securities, summarized by contractual maturities
Less than one year91,776
1 year – 5 years342,607
5 years – 10 years203,664
Greater than 10 years203,725
Total841,772
APS | Other
Nuclear decommissioning trust fund assets
Other(14,137)(17,324)
Total Unrealized Gains0 0
Total Unrealized Losses0 0
Nuclear Decommissioning Trust | APS
Nuclear decommissioning trust fund assets
Fair Value1,159,699 1,138,435
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains2,968 3,313
Realized losses(4,148)(2,227)
Proceeds from the sale of securities234,728 178,196
Nuclear Decommissioning Trust | APS | Equity securities
Nuclear decommissioning trust fund assets
Equity securities670,359 639,851
Nuclear Decommissioning Trust | APS | Available for sale-fixed income securities
Nuclear decommissioning trust fund assets
Fair Value504,878 516,412
Fair value of fixed income securities, summarized by contractual maturities
Less than one year25,048
1 year – 5 years147,347
5 years – 10 years137,479
Greater than 10 years195,004
Total504,878
Nuclear Decommissioning Trust | APS | Other
Nuclear decommissioning trust fund assets
Other(15,538)(17,828)
Other Special Use Funds | APS
Nuclear decommissioning trust fund assets
Fair Value357,506 254,509
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains0 0
Realized losses0 0
Proceeds from the sale of securities145,250 $ 16,891
Other Special Use Funds | APS | Equity securities
Nuclear decommissioning trust fund assets
Equity securities19,211 37,337
Other Special Use Funds | APS | Available for sale-fixed income securities
Nuclear decommissioning trust fund assets
Fair Value336,894 216,668
Other Special Use Funds | APS | Other
Nuclear decommissioning trust fund assets
Other1,401 $ 504
Coal Reclamation Escrow Account | APS | Available for sale-fixed income securities
Fair value of fixed income securities, summarized by contractual maturities
Less than one year26,259
1 year – 5 years34,936
5 years – 10 years2,708
Greater than 10 years8,721
Total72,624
Active union medical trust | APS | Available for sale-fixed income securities
Fair value of fixed income securities, summarized by contractual maturities
Less than one year40,469
1 year – 5 years160,324
5 years – 10 years63,477
Greater than 10 years0
Total $ 264,270

Changes in Accumulated Other _3

Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands3 Months Ended
Mar. 31, 2021Mar. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period $ 5,752,793 $ 5,553,188
OCI (loss) before reclassifications262 292
Amounts reclassified from accumulated other comprehensive loss1,022 1,225
Balance at end of period5,806,680 5,596,832
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period(60,725)(56,522)
OCI (loss) before reclassifications0 0
Amounts reclassified from accumulated other comprehensive loss1,022 1,205
Balance at end of period(59,703)(55,317)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period(2,071)(574)
OCI (loss) before reclassifications262 292
Amounts reclassified from accumulated other comprehensive loss0 20
Balance at end of period(1,809)(262)
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period(62,796)(57,096)
Balance at end of period(61,512)(55,579)
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period6,345,185 5,998,803
OCI (loss) before reclassifications292
Amounts reclassified from accumulated other comprehensive loss927 1,033
Balance at end of period6,386,275 6,040,344
APS | Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period(40,918)(34,948)
OCI (loss) before reclassifications0
Amounts reclassified from accumulated other comprehensive loss927 1,013
Balance at end of period(39,991)(33,935)
APS | Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period0 (574)
OCI (loss) before reclassifications292
Amounts reclassified from accumulated other comprehensive loss0 20
Balance at end of period0 (262)
APS | Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period(40,918)(35,522)
Balance at end of period $ (39,991) $ (34,197)

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions3 Months Ended12 Months Ended
Mar. 31, 2021Mar. 31, 2020Dec. 31, 2017
Income Tax Contingency [Line Items]
Reduction in net deferred income tax liabilities $ 1,140
Amortization of an excess deferred tax liability $ 6 $ 6
Regulatory liability, amortization period28 years 6 months
Income tax expense benefit attributable to non controlling interests $ 0
Domestic Tax Authority
Income Tax Contingency [Line Items]
Amortization of an excess deferred tax liability $ 14