N-2
N-2 - USD ($) | Jun. 16, 2023 | May 31, 2023 | Mar. 31, 2023 | Dec. 31, 2022 | Sep. 30, 2022 | Jun. 30, 2022 | Mar. 31, 2022 | Dec. 31, 2021 | Sep. 30, 2021 | Jun. 30, 2021 | |
Cover [Abstract] | |||||||||||
Entity Central Index Key | 0000883618 | ||||||||||
Amendment Flag | false | ||||||||||
Document Type | 424B2 | ||||||||||
Entity Registrant Name | Nuveen Select Tax‑Free Income Portfolio | ||||||||||
Fee Table [Abstract] | |||||||||||
Shareholder Transaction Expenses [Table Text Block] | Shareholder Transaction Expenses (as a percentage of offering price) Maximum Sales Charge 1.00 % Offering Costs Borne by the Fund (1) 0.11 % Dividend Reinvestment Plan Fees (2) $ 2.50 As a Percentage of Net Assets Attributable to Common Shares (3) Annual Expenses Management Fees 0.19 % Interest and Related Expenses from Inverse Floaters (4) 0.00 % Other Expenses (5) 0.05 % Total Annual Expenses 0.24 % (1) Assuming a Common Share offering price of $14.48 (the Fund’s closing price on the NYSE on May 31, 2023). (2) You will be charged a $2.50 service charge and pay brokerage charges if you direct State Street Bank and Trust Company, as agent for the Common Shareholders (the “Plan Agent”), to sell your Common Shares held in a dividend reinvestment account. | ||||||||||
Sales Load [Percent] | 1% | ||||||||||
Dividend Reinvestment and Cash Purchase Fees | [1] | $ 2.50 | |||||||||
Other Transaction Expenses [Abstract] | |||||||||||
Annual Expenses [Table Text Block] | Shareholder Transaction Expenses (as a percentage of offering price) Maximum Sales Charge 1.00 % Offering Costs Borne by the Fund (1) 0.11 % Dividend Reinvestment Plan Fees (2) $ 2.50 As a Percentage of Net Assets Attributable to Common Shares (3) Annual Expenses Management Fees 0.19 % Interest and Related Expenses from Inverse Floaters (4) 0.00 % Other Expenses (5) 0.05 % Total Annual Expenses 0.24 % (3) Stated as annualized percentages of average net assets attributable to Common Shares for the fiscal year ended March 31, 2023. (4) Interest and Related Expenses from Inverse Floaters also includes interest expense that arises because accounting rules require the Fund to treat interest paid by trusts issuing certain inverse floating rate investments held by the Fund as having been paid (indirectly) by the Fund. Because the Fund also recognizes a corresponding amount of interest income (also indirectly), the Fund’s net asset value, net investment income, and total return are not affected by this accounting treatment. The actual Interest and Related Expenses from Inverse Floaters incurred in the future may be higher or lower. (5) Other Expenses is based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%. See “Investment Policies and Techniques—Other Investment Companies” in the SAI. | ||||||||||
Management Fees [Percent] | [2] | 0.19% | |||||||||
Interest Expenses on Borrowings [Percent] | [2],[3] | 0% | |||||||||
Distribution/Servicing Fees [Percent] | [4] | 0.11% | |||||||||
Other Annual Expenses [Abstract] | |||||||||||
Other Annual Expenses [Percent] | [2],[5] | 0.05% | |||||||||
Total Annual Expenses [Percent] | [2] | 0.24% | |||||||||
Expense Example [Table Text Block] | Example The following example illustrates the expenses including the applicable transaction fees (referred to as the “Maximum Sales Charge” in the fee table above), if any, and estimated offering costs of $1.10 that a shareholder would pay on a $1,000 investment that is held for the time periods provided in the table. The example assumes that all dividends and other distributions are reinvested in the Fund and that the Fund’s Annual Expenses, as provided above, remain the same. The example also assumes a transaction fee of 1.00%, as a percentage of the offering price, and a 5% annual return. (1) The example should not be considered a representation of future expenses. Actual expenses may be greater or less than those shown below. 1 Year 3 Years 5 Years 10 Years $14 $ 19 $ 24 $ 41 (1) The example assumes that all dividends and distributions are reinvested at Common Share NAV. Actual expenses may be greater or less than those assumed. Moreover, the Fund’s actual rate of return may be greater or less than the hypothetical 5% return shown in the example. | ||||||||||
Expense Example, Year 01 | $ 14 | ||||||||||
Expense Example, Years 1 to 3 | 19 | ||||||||||
Expense Example, Years 1 to 5 | 24 | ||||||||||
Expense Example, Years 1 to 10 | $ 41 | ||||||||||
Purpose of Fee Table , Note [Text Block] | The purpose of the table below and the Examples below are to help you understand all fees and expenses that you, as a Common Shareholder, would bear directly or indirectly. The table shows the expenses of the Fund as a percentage of the average net assets applicable to Common Shares, and not as a percentage of total assets or Managed Assets. | ||||||||||
Basis of Transaction Fees, Note [Text Block] | as a percentage of offering price | ||||||||||
Other Expenses, Note [Text Block] | Other Expenses is based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%. See “Investment Policies and Techniques—Other Investment Companies” in the SAI. | ||||||||||
General Description of Registrant [Abstract] | |||||||||||
Investment Objectives and Practices [Text Block] | Investment Objective and Policies The Fund’s investment objective is to provide current income exempt from regular federal income tax, consistent with preservation of capital. The Fund cannot assure you that it will achieve its investment objective. The Fund’s investment objective and any investment policies identified as fundamental policies may not be changed without shareholder approval. As a fundamental policy, under normal circumstances, the Fund invests at least 80% of its Assets (as defined below) in municipal securities and other related investments, the income from which is exempt from regular federal income tax and federal alternative minimum tax (as used in this document, the term “municipal securities” refers to all such investments collectively). Additionally, as a fundamental policy, the Fund may invest up to 20% of its Managed Assets (as defined below) in AMT Bonds that pay interest that is taxable under the federal alternative minimum tax applicable to non-corporate taxpayers. Any investment by the Fund in AMT Bonds will not be counted towards meeting its 80% investment in municipal securities exempt from regular federal income tax and federal alternative minimum tax. As of April 30, 2023, the Fund had invested approximately 9% of its Managed Assets in AMT Bonds. The Fund is a long-term bond fund and, as such, will generally maintain, under normal market conditions, an investment portfolio with an overall weighted average maturity of greater than 10 years. As of April 30, 2023, the effective maturity of the Fund’s portfolio was 14.09 years. “Assets” mean the net assets of the Fund plus the amount of any borrowings for investment purposes. “Managed Assets” means the total assets of the Fund, minus the sum of its accrued liabilities (other than Fund liabilities incurred for the express purpose of creating leverage). Total assets for this purpose shall include assets attributable to the Fund’s use of leverage (whether or not those assets are reflected in the Fund’s financial statements for purposes of generally accepted accounting principles), and derivatives will be valued at their market value. See “The Fund’s Investments” for additional information on the types of securities in which the Fund may invest. The Fund may invest in various municipal securities, including municipal bonds and notes, other securities issued to finance and refinance public projects, and other related securities and derivative instruments creating exposure to municipal securities that provide for the payment of interest income that is exempt from regular federal income tax (as used in this document, the term “municipal securities” refers to all such investments collectively). See “The Fund’s Investments—Municipal Securities” for additional information on the types of municipal securities in which the Fund may invest. Municipal securities are often issued by state and local governmental entities to finance or refinance public projects, such as roads, schools, and water supply systems. Municipal securities also may be issued on behalf of private entities or for private activities, such as housing, medical and educational facility construction, or for privately owned transportation, electric utility and pollution control projects. Municipal securities may be issued on a long-term basis to provide long-term financing. The repayment of such debt may be secured generally by a pledge of the full faith and credit taxing power of the issuer, a limited or special tax, or any other revenue source, including project revenues, which may include tolls, fees and other user charges, lease payments, and mortgage payments. Municipal securities also may be issued to finance projects on a short-term interim basis, anticipating repayment with the proceeds of the later issuance of long-term debt. The Fund may purchase municipal securities in the form of bonds, notes, leases or certificates of participation; structured as callable or non‑callable; with payment forms that include fixed coupon, variable rate, zero coupon, capital appreciation bonds, floating rate securities, and inverse floating rate securities. Such municipal securities also may be acquired through investments in pooled vehicles, partnerships, or other investment companies. The Fund may invest in these types of securities, including floating rate securities and inverse floating rate securities, in order to more efficiently achieve its desired overall portfolio structure as well as enhance its ability to achieve its investment objective. The Fund also may invest in derivative instruments in pursuit of its investment objective, including inverse floating rate securities. Such instruments also include financial futures contracts, swap contracts (including interest rate and credit default swaps), options on financial futures, options on swap contracts, or other derivative instruments. The Fund may invest up to 15% of its Managed Assets in inverse floating rate securities. However, the Fund may not enter into futures contracts or related options or forward contracts, if more than 30% of the Fund’s net assets would be represented by futures contracts or more than 5% of the Fund’s net assets would be committed to initial margin deposits and premiums on futures contracts and related options. Nuveen Asset Management, LLC (“Nuveen Asset Management”), the Fund’s sub-adviser, uses derivatives to seek to enhance return, to hedge some of the risks of its investments in fixed income securities or as a substitute for a position in the underlying asset. These types of strategies may generate taxable income. See “The Fund’s Investments—Derivatives.” Under normal circumstances, as a non‑fundamental policy: • The Fund invests at least 80% of its Managed Assets in municipal securities and other related investments that at the time of investment are investment grade quality. A security is considered investment grade quality if it is rated within the four highest letter grades (BBB or Baa or better) by at least one NRSRO that rates such security (even if it is rated lower by another NRSRO), or are unrated but judged to be of comparable quality by Nuveen Asset Management. • The Fund may invest up to 20% of its Managed Assets in municipal securities that at the time of investment are rated below investment grade or are unrated by any NRSRO but judged to be of comparable quality by Nuveen Asset Management. Also, as a non‑fundamental policy, no more than 10% of the Fund’s Managed Assets may be invested in municipal securities rated below B3/B‑ or that are unrated but judged to be of comparable quality by Nuveen Asset Management. Municipal securities of below investment grade quality are regarded as having predominately speculative characteristics with respect to capacity to pay interest and repay principal, and are commonly referred to as junk bonds. See “Risk Factors—Credit and Below Investment Grade Risk.” • The Fund will not invest more than 25% of its Managed Assets in municipal securities in any one industry or in any one state of origin. • The Fund may invest up to 10% of its Managed Assets in securities of other open- or closed‑end investment companies (including exchange-traded funds (“ETFs”)) that invest primarily in municipal securities of the types in which the Fund may invest directly. • The Fund will not invest more than 50% of its Managed Assets in municipal securities that, at the time of investment, are illiquid ( i.e. See “The Fund’s Investments—Investment Objective,” and “The Fund’s Investments—Investment Policies.” As of April 30, 2023, approximately 93% of the Fund’s Managed Assets were invested in securities rated investment grade by an NRSRO (including Standard & Poor’s Corporation Ratings Group, a division of The McGraw-Hill Companies, Inc. (“S&P”), Moody’s Investors Service, Inc. (“Moody’s”) and Fitch Ratings, Inc. (“Fitch”)). The relative percentages of the value of the investments attributable to investment grade municipal securities and to below investment grade municipal securities could change over time as a result of rebalancing the Fund’s assets by Nuveen Asset Management, market value fluctuations, issuance of additional shares and other events. During temporary defensive periods or in order to keep the Fund’s cash fully invested, including during the period when the net proceeds of the offering of Common Shares are being invested, the Fund may deviate from its investment policies and objectives. During such periods, the Fund may invest up to 100% of its Managed Assets in short-term investments, including high quality, short-term securities that may be either tax‑exempt or taxable. The Fund intends to invest in taxable short-term investments only in the event that suitable tax‑exempt short-term investments are not available at reasonable prices and yields. Investment in taxable short-term investments would result in a portion of your dividends being subject to regular federal income tax, and if the proportion of taxable investments exceeded 50% of the Fund’s total assets as of the close of any quarter of the Fund’s taxable year, the Fund would not satisfy the general eligibility test that would permit it to pay exempt-interest dividends for that taxable year. Such transactions will be used solely to reduce risk. There can be no assurance that such strategies will be successful. For a more complete discussion of the Fund’s portfolio composition, see “The Fund’s Investments.” | ||||||||||
Risk Factors [Table Text Block] | RISK FACTORS Risk is inherent in all investing. Investing in any investment company security involves risk, including the risk that you may receive little or no return on your investment or even that you may lose part or all of your investment. Therefore, before investing you should consider carefully the following risks that you assume when you invest in Common Shares. Portfolio Level Risks Municipal Securities Market Risk The ability of municipal issuers to make timely payments of interest and principal may be diminished during general economic downturns and as governmental cost burdens are reallocated among federal, state and local governments. In addition, laws enacted in the future by Congress or state legislatures or referenda could extend the time for payment of principal and/or interest, or impose other constraints on enforcement of such obligations, or on the ability of municipalities to levy taxes. Further, some state and local governments have been and in the future may be subject to direct ballot referenda that could limit their financial flexibility, or their ability to levy taxes or raise revenues, which may adversely affect the marketability of notes and bonds issued by those state and local governments. Issuers of municipal securities might seek protection under the bankruptcy laws. In the event of bankruptcy of such an issuer, the Fund could experience delays in collecting principal and interest and the Fund may not, in all circumstances, be able to collect all principal and interest to which it is entitled. To enforce its rights in the event of a default in the payment of interest or repayment of principal, or both, the Fund may take possession of and manage the assets securing the issuer’s obligations on such securities, which may increase the Fund’s operating expenses. Any income derived from the Fund’s ownership or operation of such assets may not be tax‑exempt. Credit Risk Credit Spread Risk i.e., Below Investment Grade Risk If a below investment grade security goes into default, or its issuer enters bankruptcy, it might be difficult to sell that security in a timely manner at a reasonable price. The secondary market for lower grade instruments may not be as liquid as the secondary market for more highly rated instruments, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular instrument. There are fewer dealers in the market for lower grade securities than for investment grade obligations. The prices quoted by different dealers for lower grade instruments may vary significantly and the spread between the bid and ask price for such instruments is generally much larger than for higher quality instruments. Under adverse market or economic conditions, the secondary market for lower grade securities could contract further, independent of any specific adverse changes in the condition of a particular issuer, and these instruments may become illiquid. As a result, the Fund could find it more difficult to sell these instruments or may be able to sell the instruments only at prices lower than if such instruments were widely traded. Prices realized upon the sale of such lower rated or unrated instruments, under these circumstances, may be less than the prices used in calculating the Fund’s NAV. For these reasons, an investment in the Fund, compared with a portfolio consisting solely of investment grade securities, may experience the following: • increased price sensitivity resulting from a deteriorating economic environment and changing interest rates; • greater risk of loss due to default or declining credit quality; • adverse issuer specific events that are more likely to render the issuer unable to make interest and/or principal payments; and • the possibility that a negative perception of the below investment grade market develops, resulting in the price and liquidity of below investment grade securities becoming depressed, and this negative perception could last for a significant period of time. In the event that the Fund disposes of a portfolio security subsequent to its being downgraded, the Fund may experience a greater loss than if such security had been sold prior to such downgrade. Interest Rate Risk London Inter-bank Offered Rate (“LIBOR”) Transition Risk. Duration Risk Call Risk Prepayment Risk. Reinvestment Risk Alternative Minimum Tax Risk. Inverse Floating Rate Securities Risk The Fund may invest in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund. In Nuveen Fund Advisors’ and Nuveen Asset Management’s discretion, the Fund may enter into separate shortfall and forbearance agreement with the third-party granting liquidity to the floating rate security holders of the special purpose trust. The Fund may enter into such recourse agreements (i) when the liquidity provider to the special purpose trust requires such an agreement because the level of leverage in the trust exceeds the level that the liquidity provider is willing to support absent such an agreement; and/or (ii) to seek to prevent the liquidity provider from collapsing the trust in the event that the municipal obligation held in the trust has declined in value. Such an agreement would require the Fund to reimburse the third-party granting liquidity to the floating rate security holders of the special purpose trust, upon termination of the trust issuing the inverse floater, the difference between the liquidation value of the bonds held in the trust and the principal amount due to the holders of floating rate interests. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities. Inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of fixed rate securities. The Fund’s investments in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund may be highly leveraged. The structure and degree to which the Fund’s inverse floating rate securities are highly leveraged will vary based upon a number of factors, including the size of the trust itself and the terms of the underlying municipal security. In the event of a significant decline in the value of an underlying security, the Fund may suffer losses in excess of the amount of its investment (up to an amount equal to the value of the municipal securities underlying the inverse floating rate securities) as a result of liquidating special purpose trusts or other collateral required to maintain the Fund’s anticipated leverage ratio. The Fund’s investment in inverse floating rate securities creates leverage. Any leverage achieved through the Fund’s investment in inverse floating rate securities will create an opportunity for increased Common Share net income and returns, but will also create the possibility that Common Share long-term returns will be diminished if the cost of leverage exceeds the return on the inverse floating rate securities purchased by the Fund. See “Risk Factors—Fund Level and Other Risks—Leverage Risk.” The amount of fees paid to Nuveen Asset Management for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets—this may create an incentive for Nuveen Asset Management to leverage the Fund. “Managed Assets” means the total assets of the Fund, minus the sum of its accrued liabilities (other than liabilities incurred for the express purpose of creating leverage). Total assets for this purpose shall include assets attributable to the Fund’s use of leverage (whether or not those assets are reflected in the Fund’s financial statements for purposes of generally accepted accounting principles), and derivatives will be valued at their market value. Inverse floating rate securities have varying degrees of liquidity based, among other things, upon the liquidity of the underlying securities deposited in a special purpose trust. The market price of inverse floating rate securities is more volatile than the underlying securities due to leverage. The leverage attributable to such inverse floating rate securities may be “called away” on relatively short notice and therefore may be less permanent than more traditional forms of leverage. In certain circumstances, the likelihood of an increase in the volatility of NAV and market price of the Common Shares may be greater for a fund (like the Fund) that relies primarily on inverse floating rate securities to achieve a desired leverage ratio. The Fund may be required to sell its inverse floating rate securities at less than favorable prices, or liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following: • If the Fund has a need for cash and the securities in a special purpose trust are not actively trading due to adverse market conditions; • If special purpose trust sponsors (as a collective group or individually) experience financial hardship and consequently seek to terminate their respective outstanding trusts; and • If the value of an underlying security declines significantly and if additional collateral has not been posted by the Fund. There is no assurance that the Fund’s strategy of investing in inverse floating rate securities will be successful. Municipal Securities Market Liquidity Risk Special Risks Related to Certain Municipal Obligations Certificates of participation, which represent interests in unmanaged pools of municipal leases or installment contracts, involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificate of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation. Illiquid Investments Risk sold only in a privately negotiated transaction or pursuant to an exemption from registration. The Fund may not be able to readily dispose of such securities at prices that approximate those at which the Fund could sell such securities if they were more widely traded and, as a result of such illiquidity, the Fund may have to sell other investments or engage in borrowing transactions if necessary to raise cash to meet its obligations. Limited liquidity can also affect the market price of securities, thereby adversely affecting the Fund’s NAV and ability to make dividend distributions. The financial markets in general have in recent years experienced periods of extreme secondary market supply and demand imbalance, resulting in a loss of liquidity during which market prices were suddenly and substantially below traditional measures of intrinsic value. During such periods, some securities could be sold only at arbitrary prices and with substantial losses. Periods of such market dislocation may occur again at any time. Distressed Securities Risk Derivatives Risk Whether the Fund’s use of derivatives is successful will depend on, among other things, Nuveen Fund Advisors and Nuveen Asset Management correctly forecasting market circumstances, liquidity, market values, interest rates and other applicable factors. If Nuveen Fund Advisors and Nuveen Asset Management incorrectly forecast these and other factors, the investment performance of the Fund will be unfavorably affected. In addition, there can be no assurance that the derivatives investing techniques, as they may be developed and implemented by the Fund, will be successful in mitigating risk or achieving the Fund’s investment objective. The use of derivatives to enhance returns may be particularly speculative. Swap Transactions Risk The Fund generally may only close out a swap, cap, floor, collar or other two‑party contract with its particular counterparty, and generally may only transfer a position with the consent of that counterparty. Because they are two‑party contracts and because they may have terms of greater than seven days, swap agreements may be considered illiquid. In addition, the price at which the Fund may close out such a two‑party contract may not correlate with the price change in the underlying reference asset. Moreover, the Fund bears the risk of loss of the amount expected to be received under a swap agreement in the event of the default or bankruptcy of a swap agreement counterparty. If the counterparty defaults, the Fund will have contractual remedies, but there can be no assurance that the counterparty will be able to meet its contractual obligations or that the Fund will succeed in enforcing its rights. The Fund may write (sell) and purchase put and call swap options. When the Fund purchases a swap option, it risks losing only the amount of the premium it has paid should it decide to let the option expire unexercised. When the Fund writes a swap option, upon exercise of the option the Fund would become obligated according to the terms of the underlying agreement t is possible that developments in the derivatives market, including changes in government regulation, could adversely affect the Fund’s ability to terminate existing swap agreements or to realize amounts to be received under such agreements. Financial Futures and Options Transactions Risk There are certain risks associated with the use of financial futures and options to hedge investment portfolios. There may be an imperfect correlation between price movements of the futures and options and price movements of the portfolio securities being hedged. Losses may be incurred in hedging transactions, which could reduce the portfolio gains that might have been realized if the hedging transactions had not been entered into. If the Fund engages in futures transactions or in the writing of options on futures, it will be required to maintain initial margin and maintenance margin and may be required to make daily variation margin payments in accordance with applicable rules of the exchanges and the CFTC. If the Fund purchases a financial futures contract or a call option or writes a put option in order to hedge the anticipated purchase of municipal securities, and if the Fund fails to complete the anticipated purchase transaction, the Fund may have a loss or a gain on the futures or options transaction that will not be offset by price movements in the municipal securities that were the subject of the anticipatory hedge. The cost of put options on debt securities or indexes effectively increases the cost of the securities subject to them, thereby reducing the yield otherwise available from these securities. If the Fund decides to use futures contracts or options on futures contracts for hedging purposes, the Fund will be required to establish an account for such purposes with one or more CFTC-registered futures commission merchants. A futures commission merchant could establish initial and maintenance margin requirements for the Fund that are greater than those which would otherwise apply to the Fund under applicable rules of the exchanges and the CFTC. There can be no assurance that a liquid market will exist at a time when the Fund seeks to close out a derivatives or futures or a futures option position, and the Fund would remain obligated to meet margin requirements until the position is closed. Futures exchanges may limit the amount of fluctuation permitted in certain futures contract prices during a single trading day. The daily limit establishes the maximum amount that the price of the futures contract may vary either up or down from the previous day’s settlement price at the end of the current trading session. Once the daily limit has been reached in a futures contract subject to the limit, no more trades may be made on that day at a price beyond that limit. The daily limit governs only price movements during a particular trading day and therefore does not limit potential losses because the limit may work to prevent the liquidation of unfavorable positions. For example, futures prices have occasionally moved to the daily limit for several consecutive trading days with little or no trading, thereby preventing prompt liquidation of positions and subjecting some holders of futures contracts to substantial losses. Hedging Risk instruments to the Fund’s portfolio holdings or other factors. No assurance can be given that Nuveen Asset Management’s judgment in this respect will be correct. In addition, no assurance can be given that the Fund will enter into hedging or other transactions at times or under circumstances in which it may be advisable to do so. Hedging activities may reduce the Fund’s opportunities for gain by offsetting the positive effects of favorable price movements and may result in net losses. Puerto Rico Municipal Securities Market Risk Puerto Rico currently is experiencing significant fiscal and economic challenges, including substantial debt service obligations, high levels of unemployment, underfunded public retirement systems, and persistent government budget deficits. These challenges may negatively affect the value of the Fund’s investments in Puerto Rican municipal securities. Several major ratings agencies have downgraded the general obligation debt of Puerto Rico to below investment grade and continue to maintain a negative outlook for this debt, which increases the likelihood that the rating will be lowered further. In both August 2015 and January 2016, Puerto Rico defaulted on its debt by failing to make full payment due on its outstanding bonds, and there can be no assurance that Puerto Rico will be able to satisfy its future debt obligations. Further downgrades or defaults may place additional strain on the Puerto Rico economy and may negatively affect the value, liquidity, and volatility of the Fund’s investments in Puerto Rican municipal securities. Additionally, numerous issuers have entered Title III of the Puerto Rico Oversite, Management and Economic Stability Act (“PROMESA”), which is similar to bankruptcy protection, through which the Commonwealth of Puerto Rico can restructure its debt. However, Puerto Rico’s case is the first ever heard under PROMESA and there is no existing case precedent to guide the proceedings. Accordingly, Puerto Rico’s debt restructuring process could take significantly longer than traditional municipal bankruptcy proceedings. Further, it is not clear whether a debt restructuring process will ultimately be approved or, if so, the extent to which it will apply to Puerto Rico municipal securities sold by an issuer other than the territory. A debt restructuring could reduce the principal amount due, the interest rate, the maturity, and other terms of Puerto Rico municipal securities, which could adversely affect the value of Puerto Rican municipal securities. Legislation, including PROMESA that would allow Puerto Rico to restructure its municipal debt obligations, thus increasing the risk that Puerto Rico may never pay off municipal indebtedness, or may pay only a small fraction of the amount owed, could also impact the value of the Fund’s investments in Puerto Rican municipal securities. These challenges and uncertainties have been exacerbated by Hurricanes Irma and Maria and the resulting natural disaster in Puerto Rico. In September 2017, Hurricanes Irma and Maria struck Puerto Rico, causing major damage across the Commonwealth, including damage to its water, power, and telecommunications infrastructure. The length of time needed to rebuild Puerto Rico’s infrastructure is unclear, but could amount to years, during which the Commonwealth is likely to be in an uncertain economic state. The full extent of the natural disaster’s impact on Puerto Rico’s economy and foreign investment in Puerto Rico is difficult to estimate. More recently, in late December 2019 and January 2020, a series of earthquakes hit Puerto Rico, including a magnitude 6.4 earthquake, the most powerful earthquake to hit the island in more than a century, causing an estimated $200 million in damage. In addition, in early 2020, as the population of Puerto Rico worked to recover from these natural disasters, the island was significantly impacted by Covid, resulting in the Commonwealth’s authorization of a $787 million relief package to fight the pandemic and its economic impacts. Any reduction in the Commonwealth’s revenues as a result of the pandemic could have a negative ability on the Commonwealth to meet its debt service obligations, including with respect to debt held by the Fund. Puerto Rico’s political and economic conditions could have a negative impact on the liquidity or value of Puerto Rican municipal securities, and consequently may affect the Fund’s investments and its performance if the Fund invests a significant portion of its assets in Puerto Rican municipal securities. Sector Focus Risk i.e., Sector and Industry Risk. Economic Sector Risk To the extent that the Fund focuses its assets in the hospital and healthcare facilities sector, for example, the Fund will be subject to risks associated with such sector, including adverse government regulation and reduction in reimbursement rates, as well as government approval of products and services and intense competition. Securities issued with respect to special taxing districts will be subject to various risks, including real-estate development related risks and taxpayer concentration risk. Further, the fees, special taxes or tax allocations and other revenues established to secure the obligations of securities issued with respect to special taxing districts are generally limited as to the rate or amount that may be levied or assessed and are not subject to increase pursuant to rate covenants or municipal or corporate guarantees. Charter schools and other private educational facilities are subject to various risks, including the reversal of legislation authorizing or funding charter schools, the failure to renew or secure a charter, the failure of a funding entity to appropriate necessary funds and competition from alternatives such as voucher programs. Issuers of municipal utility securities can be significantly affected by government regulation, financing difficulties, supply and demand of services or fuel and natural resource conservation. The transportation sector, including airports, airlines, ports and other transportation facilities, can be significantly affected by changes in the economy, fuel prices, labor relations, insurance costs and government regulation. Income Risk Inflation Risk Deflation Risk Zero Coupon Bonds Risk Tax Risk de minimis To qualify to pay exempt-interest dividends, which are treated as items of interest excludable from gross income for federal income tax purposes, at least 50% of the value of the total assets of the Fund must consist of obligations exempt from regular income tax as of the close of each quarter of the Fund’s taxable year. If the proportion of taxable investments held by the Fund exceeds 50% of the Fund’s total assets as of the close of any quarter of any Fund taxable year, the Fund will not for that taxable year satisfy the general eligibility test that otherwise permits it to pay exempt-interest dividends. The value of the Fund’s investments and its NAV may be adversely affected by changes in tax rates and policies. Because interest income from municipal securities is normally not subject to regular federal income taxation, the attractiveness of municipal securities in relation to other investment alternatives is affected by changes in federal income tax rates or changes in the tax‑exempt status of interest income from municipal securities. Any proposed or actual changes in such rates or exempt status, therefore, can significantly affect the demand for and supply, liquidity and marketability of municipal securities. This could in turn affect the Fund’s NAV and ability to acquire and dispose of municipal securities at desirable yield and price levels. Additionally, the Fund may not be a suitable investment for tax exempt or tax‑deferred accounts or for investors who are not sensitive to the federal income tax consequences of their investments. The Fund’s investment in AMT Bonds may trigger adverse tax consequences for Fund shareholders who are subject to the federal alternative minimum tax applicable to non-corporate taxpayers. If you are, or as a result of investment in the Fund would become, subject to the federal alternative minimum tax, the Fund may not be a suitable investment for you. In addition, distributions of taxable ordinary income (including any net short-term capital gain) will be taxable to shareholders as ordinary income (and not eligible for favorable taxation as “qualified dividend income”), and capital gain dividends will be taxable as long-term capital gains. The portion of each distribution attributable to capital appreciation is expected to be higher than that in a typical municipal bond fund. As a result, the level of taxable distributions currently anticipated by the Fund could be significant for Common Shareholders. Unlike a distribution attributable to tax-exempt income, a distribution attributable to capital appreciation would be subject to tax depending on a shareholder’s situation. Interest income on municipal securities also may be subject to state and local income taxes. See “Tax Matters.” Taxability Risk Insurance Risk Tobacco Settlement Bond Risk Valuation Risk Other Investment Companies Risk shares may exceed the costs of investing directly in its underlying investments. Nuveen Fund Advisors will take expenses into account when evaluating the investment merits of an investment in an investment company relative to available municipal security investments. The Fund will consider the investments of underlying investment companies when determining compliance with Rule 35d‑1 under the 1940 Act. Moreover, the Fund will consider the investments of underlying investment companies when determining compliance with its own concentration policy, to the extent the Fund has sufficient information about such investments. In addition, securities of other investment companies may be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities and therefore magnify the Fund’s leverage risk. As described in the Fund’s Prospectus, the NAV and market value of leveraged shares will be more volatile and the yield to Common Shareholders will tend to fluctuate more than the yield generated by unleveraged shares. With respect to ETFs, an ETF that is based on a specific index may not be able to replicate and maintain exactly the composition and relative weighting of securities in the index. The value of an ETF based on a specific index is subject to change as the values of its respective component assets fluctuate according to market volatility. ETFs typically rely on a limited pool of authorized participants to create and redeem shares, and an active trading market for ETF shares may not develop or be maintained. The market value of shares of ETFs and closed‑end funds may differ from their NAV. Fund Level and Other Risks Market Discount from Net Asset Value Investment and Market Risk Leverage Risk The Fund will pay (and Common Shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the net asset value of and net income payable with respect to the Common Shares. Because of the costs of leverage, the Fund may incur losses even if the Fund has positive returns if they are not sufficient to cover the costs of leverage. Nuveen Fund Advisors, based on its assessment of market conditions, may increase or decrease the Fund’s level of leverage. Such changes may impact the Fund’s distributions and the valuation of the Common Shares in the secondary market. There is no assurance that the Fund will continue to utilize leverage or that the Fund’s use of leverage will be successful. Furthermore, the amount of fees paid to Nuveen Fund Advisors and Nuveen Asset Management for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets, which may create an incentive for Nuveen Fund Advisors to leverage the Fund or increase the Fund’s leverage. Certain types of leverage used by the Fund may result in the Fund being subject to certain covenants, asset coverage or other portfolio composition limits by its lenders, liquidity providers, or reverse repurchase counterparties. Such limitations may be more stringent than those imposed by the 1940 Act and may affect whether the Fund is able to maintain its desired amount of leverage. At this time, Nuveen Fund Advisors does not believe that any such potential investment limitations will impede it from managing the Fund’s portfolio in accordance with its investment objectives and policies. See “Use of Leverage.” The Fund may invest in the securities of other investment companies, which may themselves be leveraged and therefore present similar risks to those described above and magnify the Fund’s leverage risk. The risk of loss attributable to the Fund’s use of leverage is borne by Common Shareholders. Litigation Risk Global Economic Risk Additionally, unexpected events and their aftermaths, including broad financial dislocations (such as the “great recession” of 2008‑09), war, armed conflict (such as Russia’s invasion of Ukraine in February of 2022), terrorism, the imposition of economic sanctions, natural and environmental disasters and the spread of infectious illnesses or other public health emergencies (such as the COVID‑19 coronavirus pandemic first detected in December of 2019), may adversely affect the global economy and the markets and issuers in which the Fund invests. These events could reduce consumer demand or economic output, result in market closure, travel restrictions or quarantines, or wide-spread unemployment, and generally have a severe negative impact on the global economy. Such events could also impair the information technology and other operational systems upon which the Fund’s service providers, including Nuveen Fund Advisors and Nuveen Asset Management, rely, and could otherwise disrupt the ability of employees of the Fund’s service providers to perform essential tasks on behalf of the Fund. Furthermore, such events could cause financial markets to experience elevated or even extreme volatility and losses, and could result in the disruption of trading and the reduction of liquidity in many instruments. In addition, sanctions and other measures could limit or prevent the Fund from buying and selling securities (in sanctioned countries and other markets), significantly delay or prevent the settlement of securities transactions, and significantly impact liquidity and performance. Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. In addition, there is a possibility that the rising prices of goods and services may have an effect on the Fund. As inflation increases, the value of the Fund’s assets may decline. Legislation and Regulatory Risk The SEC’s recently adopted Rule 18f‑4 under the 1940 Act, governing the use of derivatives by registered investment companies, could affect the nature and extent of derivatives used by the Fund. The full impact of such rules is uncertain at this time. Rule 18f‑4 could limit the implementation of the Fund’s use of derivatives, which could have an adverse impact on the Fund. Anti-Takeover Provisions Potential Conflicts of Interest Risk Economic and Political Events Risk Cybersecurity Risk Unrated Securities Risk Counterparty Risk The counterparty risk for cleared derivatives is generally lower than for uncleared OTC derivative transactions. In a cleared derivative transaction, generally, a clearing organization becomes substituted for each counterparty to a cleared derivative contract and each party to a trade looks only to the clear | ||||||||||
Share Price [Table Text Block] | TRADING AND NET ASSET VALUE INFORMATION The following table shows for the periods indicated: (i) the high and low sales prices for the Common Shares reported as of the end of the day on the NYSE, (ii) the high and low net asset values of the Common Shares, and (iii) the high and low of the premium/(discount) to net asset value (expressed as a percentage) of the Common Shares. Price Net Asset Value Premium/ (Discount) Fiscal Quarter Ended High Low High Low High Low March 2023 $ 14.85 $ 13.91 $ 14.75 $ 14.26 2.17 % (3.34 )% December 2022 $ 14.06 $ 12.91 $ 14.48 $ 13.63 (2.16 )% (7.19 )% September 2022 $ 14.41 $ 12.96 $ 14.91 $ 13.82 (1.33 )% (6.49 )% June 2022 $ 14.45 $ 13.24 $ 15.15 $ 14.28 (2.76 )% (7.35 )% March 2022 $ 15.98 $ 14.17 $ 16.39 $ 15.06 (2.44 )% (6.44 )% December 2021 $ 17.32 $ 15.73 $ 16.40 $ 16.24 6.00 % (3.91 )% September 2021 $ 18.72 $ 16.75 $ 16.66 $ 16.34 12.84 % 1.39 % June 2021 $ 18.55 $ 16.95 $ 16.62 $ 16.36 12.49 % 2.98 % The net asset value per Common Share, the market price and percent of premium/(discount) to net asset value per common share on May 31, 2023 were $14.36, $14.48, and 0.84%, respectively. As of May 31, 2023, the Fund had 46,810,046 Common Shares outstanding and net assets applicable to Common Shares of $672,389,842. | ||||||||||
Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |||||||||||
Outstanding Securities [Table Text Block] | The following provides information about the Fund’s outstanding Common Shares as of May 31, 2023: Title of Class Amount Amount by the for its Amount Common unlimited — 46,810,046 | ||||||||||
Municipal Securities Market Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Municipal Securities Market Risk The ability of municipal issuers to make timely payments of interest and principal may be diminished during general economic downturns and as governmental cost burdens are reallocated among federal, state and local governments. In addition, laws enacted in the future by Congress or state legislatures or referenda could extend the time for payment of principal and/or interest, or impose other constraints on enforcement of such obligations, or on the ability of municipalities to levy taxes. Further, some state and local governments have been and in the future may be subject to direct ballot referenda that could limit their financial flexibility, or their ability to levy taxes or raise revenues, which may adversely affect the marketability of notes and bonds issued by those state and local governments. Issuers of municipal securities might seek protection under the bankruptcy laws. In the event of bankruptcy of such an issuer, the Fund could experience delays in collecting principal and interest and the Fund may not, in all circumstances, be able to collect all principal and interest to which it is entitled. To enforce its rights in the event of a default in the payment of interest or repayment of principal, or both, the Fund may take possession of and manage the assets securing the issuer’s obligations on such securities, which may increase the Fund’s operating expenses. Any income derived from the Fund’s ownership or operation of such assets may not be tax‑exempt. | ||||||||||
Credit Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Credit Risk | ||||||||||
Credit Spread Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Credit Spread Risk i.e., | ||||||||||
Below Investment Grade Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Below Investment Grade Risk If a below investment grade security goes into default, or its issuer enters bankruptcy, it might be difficult to sell that security in a timely manner at a reasonable price. The secondary market for lower grade instruments may not be as liquid as the secondary market for more highly rated instruments, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular instrument. There are fewer dealers in the market for lower grade securities than for investment grade obligations. The prices quoted by different dealers for lower grade instruments may vary significantly and the spread between the bid and ask price for such instruments is generally much larger than for higher quality instruments. Under adverse market or economic conditions, the secondary market for lower grade securities could contract further, independent of any specific adverse changes in the condition of a particular issuer, and these instruments may become illiquid. As a result, the Fund could find it more difficult to sell these instruments or may be able to sell the instruments only at prices lower than if such instruments were widely traded. Prices realized upon the sale of such lower rated or unrated instruments, under these circumstances, may be less than the prices used in calculating the Fund’s NAV. For these reasons, an investment in the Fund, compared with a portfolio consisting solely of investment grade securities, may experience the following: • increased price sensitivity resulting from a deteriorating economic environment and changing interest rates; • greater risk of loss due to default or declining credit quality; • adverse issuer specific events that are more likely to render the issuer unable to make interest and/or principal payments; and • the possibility that a negative perception of the below investment grade market develops, resulting in the price and liquidity of below investment grade securities becoming depressed, and this negative perception could last for a significant period of time. In the event that the Fund disposes of a portfolio security subsequent to its being downgraded, the Fund may experience a greater loss than if such security had been sold prior to such downgrade. | ||||||||||
Interest Rate Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Interest Rate Risk | ||||||||||
London Inter bank Offered Rate LIBOR Transition Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | London Inter-bank Offered Rate (“LIBOR”) Transition Risk. | ||||||||||
Duration Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Duration Risk | ||||||||||
Call Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Call Risk | ||||||||||
Prepayment Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Prepayment Risk. | ||||||||||
Reinvestment Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Reinvestment Risk | ||||||||||
Alternative Minimum Tax Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Alternative Minimum Tax Risk. | ||||||||||
Inverse Floating Rate Securities Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Inverse Floating Rate Securities Risk The Fund may invest in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund. In Nuveen Fund Advisors’ and Nuveen Asset Management’s discretion, the Fund may enter into separate shortfall and forbearance agreement with the third-party granting liquidity to the floating rate security holders of the special purpose trust. The Fund may enter into such recourse agreements (i) when the liquidity provider to the special purpose trust requires such an agreement because the level of leverage in the trust exceeds the level that the liquidity provider is willing to support absent such an agreement; and/or (ii) to seek to prevent the liquidity provider from collapsing the trust in the event that the municipal obligation held in the trust has declined in value. Such an agreement would require the Fund to reimburse the third-party granting liquidity to the floating rate security holders of the special purpose trust, upon termination of the trust issuing the inverse floater, the difference between the liquidation value of the bonds held in the trust and the principal amount due to the holders of floating rate interests. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities. Inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of fixed rate securities. The Fund’s investments in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund may be highly leveraged. The structure and degree to which the Fund’s inverse floating rate securities are highly leveraged will vary based upon a number of factors, including the size of the trust itself and the terms of the underlying municipal security. In the event of a significant decline in the value of an underlying security, the Fund may suffer losses in excess of the amount of its investment (up to an amount equal to the value of the municipal securities underlying the inverse floating rate securities) as a result of liquidating special purpose trusts or other collateral required to maintain the Fund’s anticipated leverage ratio. The Fund’s investment in inverse floating rate securities creates leverage. Any leverage achieved through the Fund’s investment in inverse floating rate securities will create an opportunity for increased Common Share net income and returns, but will also create the possibility that Common Share long-term returns will be diminished if the cost of leverage exceeds the return on the inverse floating rate securities purchased by the Fund. See “Risk Factors—Fund Level and Other Risks—Leverage Risk.” The amount of fees paid to Nuveen Asset Management for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets—this may create an incentive for Nuveen Asset Management to leverage the Fund. “Managed Assets” means the total assets of the Fund, minus the sum of its accrued liabilities (other than liabilities incurred for the express purpose of creating leverage). Total assets for this purpose shall include assets attributable to the Fund’s use of leverage (whether or not those assets are reflected in the Fund’s financial statements for purposes of generally accepted accounting principles), and derivatives will be valued at their market value. Inverse floating rate securities have varying degrees of liquidity based, among other things, upon the liquidity of the underlying securities deposited in a special purpose trust. The market price of inverse floating rate securities is more volatile than the underlying securities due to leverage. The leverage attributable to such inverse floating rate securities may be “called away” on relatively short notice and therefore may be less permanent than more traditional forms of leverage. In certain circumstances, the likelihood of an increase in the volatility of NAV and market price of the Common Shares may be greater for a fund (like the Fund) that relies primarily on inverse floating rate securities to achieve a desired leverage ratio. The Fund may be required to sell its inverse floating rate securities at less than favorable prices, or liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following: • If the Fund has a need for cash and the securities in a special purpose trust are not actively trading due to adverse market conditions; • If special purpose trust sponsors (as a collective group or individually) experience financial hardship and consequently seek to terminate their respective outstanding trusts; and • If the value of an underlying security declines significantly and if additional collateral has not been posted by the Fund. There is no assurance that the Fund’s strategy of investing in inverse floating rate securities will be successful. | ||||||||||
Municipal Securities Market Liquidity Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Municipal Securities Market Liquidity Risk | ||||||||||
Special Risks Related to Certain Municipal Obligations [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Special Risks Related to Certain Municipal Obligations Certificates of participation, which represent interests in unmanaged pools of municipal leases or installment contracts, involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificate of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation. | ||||||||||
Illiquid Investments Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Illiquid Investments Risk sold only in a privately negotiated transaction or pursuant to an exemption from registration. The Fund may not be able to readily dispose of such securities at prices that approximate those at which the Fund could sell such securities if they were more widely traded and, as a result of such illiquidity, the Fund may have to sell other investments or engage in borrowing transactions if necessary to raise cash to meet its obligations. Limited liquidity can also affect the market price of securities, thereby adversely affecting the Fund’s NAV and ability to make dividend distributions. The financial markets in general have in recent years experienced periods of extreme secondary market supply and demand imbalance, resulting in a loss of liquidity during which market prices were suddenly and substantially below traditional measures of intrinsic value. During such periods, some securities could be sold only at arbitrary prices and with substantial losses. Periods of such market dislocation may occur again at any time. | ||||||||||
Distressed Securities Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Distressed Securities Risk | ||||||||||
Derivatives Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Derivatives Risk Whether the Fund’s use of derivatives is successful will depend on, among other things, Nuveen Fund Advisors and Nuveen Asset Management correctly forecasting market circumstances, liquidity, market values, interest rates and other applicable factors. If Nuveen Fund Advisors and Nuveen Asset Management incorrectly forecast these and other factors, the investment performance of the Fund will be unfavorably affected. In addition, there can be no assurance that the derivatives investing techniques, as they may be developed and implemented by the Fund, will be successful in mitigating risk or achieving the Fund’s investment objective. The use of derivatives to enhance returns may be particularly speculative. | ||||||||||
Swap Transactions Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Swap Transactions Risk The Fund generally may only close out a swap, cap, floor, collar or other two‑party contract with its particular counterparty, and generally may only transfer a position with the consent of that counterparty. Because they are two‑party contracts and because they may have terms of greater than seven days, swap agreements may be considered illiquid. In addition, the price at which the Fund may close out such a two‑party contract may not correlate with the price change in the underlying reference asset. Moreover, the Fund bears the risk of loss of the amount expected to be received under a swap agreement in the event of the default or bankruptcy of a swap agreement counterparty. If the counterparty defaults, the Fund will have contractual remedies, but there can be no assurance that the counterparty will be able to meet its contractual obligations or that the Fund will succeed in enforcing its rights. The Fund may write (sell) and purchase put and call swap options. When the Fund purchases a swap option, it risks losing only the amount of the premium it has paid should it decide to let the option expire unexercised. When the Fund writes a swap option, upon exercise of the option the Fund would become obligated according to the terms of the underlying agreement t is possible that developments in the derivatives market, including changes in government regulation, could adversely affect the Fund’s ability to terminate existing swap agreements or to realize amounts to be received under such agreements. | ||||||||||
Financial Futures and Options Transactions Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Financial Futures and Options Transactions Risk There are certain risks associated with the use of financial futures and options to hedge investment portfolios. There may be an imperfect correlation between price movements of the futures and options and price movements of the portfolio securities being hedged. Losses may be incurred in hedging transactions, which could reduce the portfolio gains that might have been realized if the hedging transactions had not been entered into. If the Fund engages in futures transactions or in the writing of options on futures, it will be required to maintain initial margin and maintenance margin and may be required to make daily variation margin payments in accordance with applicable rules of the exchanges and the CFTC. If the Fund purchases a financial futures contract or a call option or writes a put option in order to hedge the anticipated purchase of municipal securities, and if the Fund fails to complete the anticipated purchase transaction, the Fund may have a loss or a gain on the futures or options transaction that will not be offset by price movements in the municipal securities that were the subject of the anticipatory hedge. The cost of put options on debt securities or indexes effectively increases the cost of the securities subject to them, thereby reducing the yield otherwise available from these securities. If the Fund decides to use futures contracts or options on futures contracts for hedging purposes, the Fund will be required to establish an account for such purposes with one or more CFTC-registered futures commission merchants. A futures commission merchant could establish initial and maintenance margin requirements for the Fund that are greater than those which would otherwise apply to the Fund under applicable rules of the exchanges and the CFTC. There can be no assurance that a liquid market will exist at a time when the Fund seeks to close out a derivatives or futures or a futures option position, and the Fund would remain obligated to meet margin requirements until the position is closed. Futures exchanges may limit the amount of fluctuation permitted in certain futures contract prices during a single trading day. The daily limit establishes the maximum amount that the price of the futures contract may vary either up or down from the previous day’s settlement price at the end of the current trading session. Once the daily limit has been reached in a futures contract subject to the limit, no more trades may be made on that day at a price beyond that limit. The daily limit governs only price movements during a particular trading day and therefore does not limit potential losses because the limit may work to prevent the liquidation of unfavorable positions. For example, futures prices have occasionally moved to the daily limit for several consecutive trading days with little or no trading, thereby preventing prompt liquidation of positions and subjecting some holders of futures contracts to substantial losses. | ||||||||||
Hedging Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Hedging Risk instruments to the Fund’s portfolio holdings or other factors. No assurance can be given that Nuveen Asset Management’s judgment in this respect will be correct. In addition, no assurance can be given that the Fund will enter into hedging or other transactions at times or under circumstances in which it may be advisable to do so. Hedging activities may reduce the Fund’s opportunities for gain by offsetting the positive effects of favorable price movements and may result in net losses. | ||||||||||
Puerto Rico Municipal Securities Market Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Puerto Rico Municipal Securities Market Risk Puerto Rico currently is experiencing significant fiscal and economic challenges, including substantial debt service obligations, high levels of unemployment, underfunded public retirement systems, and persistent government budget deficits. These challenges may negatively affect the value of the Fund’s investments in Puerto Rican municipal securities. Several major ratings agencies have downgraded the general obligation debt of Puerto Rico to below investment grade and continue to maintain a negative outlook for this debt, which increases the likelihood that the rating will be lowered further. In both August 2015 and January 2016, Puerto Rico defaulted on its debt by failing to make full payment due on its outstanding bonds, and there can be no assurance that Puerto Rico will be able to satisfy its future debt obligations. Further downgrades or defaults may place additional strain on the Puerto Rico economy and may negatively affect the value, liquidity, and volatility of the Fund’s investments in Puerto Rican municipal securities. Additionally, numerous issuers have entered Title III of the Puerto Rico Oversite, Management and Economic Stability Act (“PROMESA”), which is similar to bankruptcy protection, through which the Commonwealth of Puerto Rico can restructure its debt. However, Puerto Rico’s case is the first ever heard under PROMESA and there is no existing case precedent to guide the proceedings. Accordingly, Puerto Rico’s debt restructuring process could take significantly longer than traditional municipal bankruptcy proceedings. Further, it is not clear whether a debt restructuring process will ultimately be approved or, if so, the extent to which it will apply to Puerto Rico municipal securities sold by an issuer other than the territory. A debt restructuring could reduce the principal amount due, the interest rate, the maturity, and other terms of Puerto Rico municipal securities, which could adversely affect the value of Puerto Rican municipal securities. Legislation, including PROMESA that would allow Puerto Rico to restructure its municipal debt obligations, thus increasing the risk that Puerto Rico may never pay off municipal indebtedness, or may pay only a small fraction of the amount owed, could also impact the value of the Fund’s investments in Puerto Rican municipal securities. These challenges and uncertainties have been exacerbated by Hurricanes Irma and Maria and the resulting natural disaster in Puerto Rico. In September 2017, Hurricanes Irma and Maria struck Puerto Rico, causing major damage across the Commonwealth, including damage to its water, power, and telecommunications infrastructure. The length of time needed to rebuild Puerto Rico’s infrastructure is unclear, but could amount to years, during which the Commonwealth is likely to be in an uncertain economic state. The full extent of the natural disaster’s impact on Puerto Rico’s economy and foreign investment in Puerto Rico is difficult to estimate. More recently, in late December 2019 and January 2020, a series of earthquakes hit Puerto Rico, including a magnitude 6.4 earthquake, the most powerful earthquake to hit the island in more than a century, causing an estimated $200 million in damage. In addition, in early 2020, as the population of Puerto Rico worked to recover from these natural disasters, the island was significantly impacted by Covid, resulting in the Commonwealth’s authorization of a $787 million relief package to fight the pandemic and its economic impacts. Any reduction in the Commonwealth’s revenues as a result of the pandemic could have a negative ability on the Commonwealth to meet its debt service obligations, including with respect to debt held by the Fund. Puerto Rico’s political and economic conditions could have a negative impact on the liquidity or value of Puerto Rican municipal securities, and consequently may affect the Fund’s investments and its performance if the Fund invests a significant portion of its assets in Puerto Rican municipal securities. | ||||||||||
Sector Focus Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Sector Focus Risk i.e., | ||||||||||
Sector and Industry Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Sector and Industry Risk. | ||||||||||
Economic Sector Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Economic Sector Risk To the extent that the Fund focuses its assets in the hospital and healthcare facilities sector, for example, the Fund will be subject to risks associated with such sector, including adverse government regulation and reduction in reimbursement rates, as well as government approval of products and services and intense competition. Securities issued with respect to special taxing districts will be subject to various risks, including real-estate development related risks and taxpayer concentration risk. Further, the fees, special taxes or tax allocations and other revenues established to secure the obligations of securities issued with respect to special taxing districts are generally limited as to the rate or amount that may be levied or assessed and are not subject to increase pursuant to rate covenants or municipal or corporate guarantees. Charter schools and other private educational facilities are subject to various risks, including the reversal of legislation authorizing or funding charter schools, the failure to renew or secure a charter, the failure of a funding entity to appropriate necessary funds and competition from alternatives such as voucher programs. Issuers of municipal utility securities can be significantly affected by government regulation, financing difficulties, supply and demand of services or fuel and natural resource conservation. The transportation sector, including airports, airlines, ports and other transportation facilities, can be significantly affected by changes in the economy, fuel prices, labor relations, insurance costs and government regulation. | ||||||||||
Income Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Income Risk | ||||||||||
Inflation Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Inflation Risk | ||||||||||
Deflation Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Deflation Risk | ||||||||||
Zero Coupon Bonds Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Zero Coupon Bonds Risk | ||||||||||
Tax Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Tax Risk de minimis To qualify to pay exempt-interest dividends, which are treated as items of interest excludable from gross income for federal income tax purposes, at least 50% of the value of the total assets of the Fund must consist of obligations exempt from regular income tax as of the close of each quarter of the Fund’s taxable year. If the proportion of taxable investments held by the Fund exceeds 50% of the Fund’s total assets as of the close of any quarter of any Fund taxable year, the Fund will not for that taxable year satisfy the general eligibility test that otherwise permits it to pay exempt-interest dividends. The value of the Fund’s investments and its NAV may be adversely affected by changes in tax rates and policies. Because interest income from municipal securities is normally not subject to regular federal income taxation, the attractiveness of municipal securities in relation to other investment alternatives is affected by changes in federal income tax rates or changes in the tax‑exempt status of interest income from municipal securities. Any proposed or actual changes in such rates or exempt status, therefore, can significantly affect the demand for and supply, liquidity and marketability of municipal securities. This could in turn affect the Fund’s NAV and ability to acquire and dispose of municipal securities at desirable yield and price levels. Additionally, the Fund may not be a suitable investment for tax exempt or tax‑deferred accounts or for investors who are not sensitive to the federal income tax consequences of their investments. The Fund’s investment in AMT Bonds may trigger adverse tax consequences for Fund shareholders who are subject to the federal alternative minimum tax applicable to non-corporate taxpayers. If you are, or as a result of investment in the Fund would become, subject to the federal alternative minimum tax, the Fund may not be a suitable investment for you. In addition, distributions of taxable ordinary income (including any net short-term capital gain) will be taxable to shareholders as ordinary income (and not eligible for favorable taxation as “qualified dividend income”), and capital gain dividends will be taxable as long-term capital gains. The portion of each distribution attributable to capital appreciation is expected to be higher than that in a typical municipal bond fund. As a result, the level of taxable distributions currently anticipated by the Fund could be significant for Common Shareholders. Unlike a distribution attributable to tax-exempt income, a distribution attributable to capital appreciation would be subject to tax depending on a shareholder’s situation. Interest income on municipal securities also may be subject to state and local income taxes. See “Tax Matters.” | ||||||||||
Taxability Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Taxability Risk | ||||||||||
Insurance Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Insurance Risk | ||||||||||
Tobacco Settlement Bond Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Tobacco Settlement Bond Risk | ||||||||||
Valuation Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Valuation Risk | ||||||||||
Other Investment Companies Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Other Investment Companies Risk shares may exceed the costs of investing directly in its underlying investments. Nuveen Fund Advisors will take expenses into account when evaluating the investment merits of an investment in an investment company relative to available municipal security investments. The Fund will consider the investments of underlying investment companies when determining compliance with Rule 35d‑1 under the 1940 Act. Moreover, the Fund will consider the investments of underlying investment companies when determining compliance with its own concentration policy, to the extent the Fund has sufficient information about such investments. In addition, securities of other investment companies may be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities and therefore magnify the Fund’s leverage risk. As described in the Fund’s Prospectus, the NAV and market value of leveraged shares will be more volatile and the yield to Common Shareholders will tend to fluctuate more than the yield generated by unleveraged shares. With respect to ETFs, an ETF that is based on a specific index may not be able to replicate and maintain exactly the composition and relative weighting of securities in the index. The value of an ETF based on a specific index is subject to change as the values of its respective component assets fluctuate according to market volatility. ETFs typically rely on a limited pool of authorized participants to create and redeem shares, and an active trading market for ETF shares may not develop or be maintained. The market value of shares of ETFs and closed‑end funds may differ from their NAV. | ||||||||||
Market Discount from Net Asset Value [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Market Discount from Net Asset Value | ||||||||||
Investment and Market Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Investment and Market Risk | ||||||||||
Leverage Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Leverage Risk The Fund will pay (and Common Shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the net asset value of and net income payable with respect to the Common Shares. Because of the costs of leverage, the Fund may incur losses even if the Fund has positive returns if they are not sufficient to cover the costs of leverage. Nuveen Fund Advisors, based on its assessment of market conditions, may increase or decrease the Fund’s level of leverage. Such changes may impact the Fund’s distributions and the valuation of the Common Shares in the secondary market. There is no assurance that the Fund will continue to utilize leverage or that the Fund’s use of leverage will be successful. Furthermore, the amount of fees paid to Nuveen Fund Advisors and Nuveen Asset Management for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets, which may create an incentive for Nuveen Fund Advisors to leverage the Fund or increase the Fund’s leverage. Certain types of leverage used by the Fund may result in the Fund being subject to certain covenants, asset coverage or other portfolio composition limits by its lenders, liquidity providers, or reverse repurchase counterparties. Such limitations may be more stringent than those imposed by the 1940 Act and may affect whether the Fund is able to maintain its desired amount of leverage. At this time, Nuveen Fund Advisors does not believe that any such potential investment limitations will impede it from managing the Fund’s portfolio in accordance with its investment objectives and policies. See “Use of Leverage.” The Fund may invest in the securities of other investment companies, which may themselves be leveraged and therefore present similar risks to those described above and magnify the Fund’s leverage risk. The risk of loss attributable to the Fund’s use of leverage is borne by Common Shareholders. | ||||||||||
Litigation Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Litigation Risk | ||||||||||
Global Economic Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Global Economic Risk Additionally, unexpected events and their aftermaths, including broad financial dislocations (such as the “great recession” of 2008‑09), war, armed conflict (such as Russia’s invasion of Ukraine in February of 2022), terrorism, the imposition of economic sanctions, natural and environmental disasters and the spread of infectious illnesses or other public health emergencies (such as the COVID‑19 coronavirus pandemic first detected in December of 2019), may adversely affect the global economy and the markets and issuers in which the Fund invests. These events could reduce consumer demand or economic output, result in market closure, travel restrictions or quarantines, or wide-spread unemployment, and generally have a severe negative impact on the global economy. Such events could also impair the information technology and other operational systems upon which the Fund’s service providers, including Nuveen Fund Advisors and Nuveen Asset Management, rely, and could otherwise disrupt the ability of employees of the Fund’s service providers to perform essential tasks on behalf of the Fund. Furthermore, such events could cause financial markets to experience elevated or even extreme volatility and losses, and could result in the disruption of trading and the reduction of liquidity in many instruments. In addition, sanctions and other measures could limit or prevent the Fund from buying and selling securities (in sanctioned countries and other markets), significantly delay or prevent the settlement of securities transactions, and significantly impact liquidity and performance. Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. In addition, there is a possibility that the rising prices of goods and services may have an effect on the Fund. As inflation increases, the value of the Fund’s assets may decline. | ||||||||||
Legislation and Regulatory Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Legislation and Regulatory Risk The SEC’s recently adopted Rule 18f‑4 under the 1940 Act, governing the use of derivatives by registered investment companies, could affect the nature and extent of derivatives used by the Fund. The full impact of such rules is uncertain at this time. Rule 18f‑4 could limit the implementation of the Fund’s use of derivatives, which could have an adverse impact on the Fund. | ||||||||||
Anti Takeover Provisions [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Anti-Takeover Provisions | ||||||||||
Potential Conflicts of Interest Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Potential Conflicts of Interest Risk | ||||||||||
Economic and Political Events Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Economic and Political Events Risk | ||||||||||
Cybersecurity Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Cybersecurity Risk | ||||||||||
Unrated Securities Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Unrated Securities Risk | ||||||||||
Counterparty Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Counterparty Risk The counterparty risk for cleared derivatives is generally lower than for uncleared OTC derivative transactions. In a cleared derivative transaction, generally, a clearing organization becomes substituted for each counterparty to a cleared derivative contract and each party to a trade looks only to the clearing organization for performance of financial obligations under the derivative contract. In effect, the clearing organization guarantees a party’s performance under the contract. However, there can be no assurance that a clearing organization, or its members, will satisfy its obligations to the Fund, or that the Fund would be able to recover the full amount of assets deposited on its behalf with the clearing organization in the event of the default by the clearing organization or the Fund’s clearing broker. In addition, cleared derivative transactions benefit from daily marking‑to‑market and settlement, and minimum capital requirements applicable to intermediaries. Uncleared OTC derivative transactions generally do not benefit from such protections. As a result, for uncleared OTC derivative transactions, there is the risk that a counterparty will not settle a transaction in accordance with its terms and conditions because of a dispute over the terms of the contract (whether or not bona fide) or because of a credit or liquidity problem, thus causing the Fund to suffer a loss. This risk is heightened for contracts with longer maturities where events may intervene to prevent settlement, or where the Fund has concentrated its transactions with a single or small group of counterparties. | ||||||||||
Risks Related to the Funds Clearing Broker and Central Clearing Counterparty [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Risks Related to the Fund’s Clearing Broker and Central Clearing Counterparty Similarly, the CEA requires a clearing organization approved by the CFTC as a derivatives clearing organization to segregate all funds and other property received from a clearing member’s clients in connection with domestic cleared derivative contracts from any funds held at the clearing organization to support the clearing member’s proprietary trading. Nevertheless, all customer funds held at a clearing organization in connection with any futures contracts are held in a commingled omnibus account and are not identified to the name of the clearing member’s individual customers. All customer funds held at a clearing organization with respect to cleared swaps of customers of a clearing broker are also held in an omnibus account, but CFTC rules require that the clearing broker notify the clearing organization of the amount of the initial margin provided by the clearing broker to the clearing organization that is attributable to each customer. With respect to futures and options contracts, a clearing organization may use assets of a non‑defaulting customer held in an omnibus account at the clearing organization to satisfy payment obligations of a defaulting customer of the clearing member to the clearing organization. With respect to cleared swaps, a clearing organization generally cannot do so, but may do so if the clearing member does not provide accurate reporting to the clearing organization as to the attribution of margin among its clients. Also, since clearing brokers generally provide to clearing organizations the net amount of variation margin required for cleared swaps for all of its customers in the aggregate, rather than the gross amount of each customer, the Fund is subject to the risk that a clearing organization will not make variation margin payments owed to the Fund if another customer of the clearing member has suffered a loss and is in default. As a result, in the event of a default or the clearing broker’s other clients or the clearing broker’s failure to extend its own funds in connection with any such default, the Fund may not be able to recover the full amount of assets deposited by the clearing broker on behalf of the Fund with the clearing organization. | ||||||||||
Portfolio Turnover Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Portfolio Turnover Risk | ||||||||||
Rating Agencies Risk [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Risk [Text Block] | Rating Agencies Risk | ||||||||||
Common Shares [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Lowest Price or Bid | $ 13.91 | $ 12.91 | $ 12.96 | $ 13.24 | $ 14.17 | $ 15.73 | $ 16.75 | $ 16.95 | |||
Highest Price or Bid | 14.85 | 14.06 | 14.41 | 14.45 | 15.98 | 17.32 | 18.72 | 18.55 | |||
Lowest Price or Bid, NAV | 14.26 | 13.63 | 13.82 | 14.28 | 15.06 | 16.24 | 16.34 | 16.36 | |||
Highest Price or Bid, NAV | $ 14.75 | $ 14.48 | $ 14.91 | $ 15.15 | $ 16.39 | $ 16.40 | $ 16.66 | $ 16.62 | |||
Highest Price or Bid, Premium (Discount) to NAV [Percent] | 2.17% | (2.16%) | (1.33%) | (2.76%) | (2.44%) | 6% | 12.84% | 12.49% | |||
Lowest Price or Bid, Premium (Discount) to NAV [Percent] | (3.34%) | (7.19%) | (6.49%) | (7.35%) | (6.44%) | (3.91%) | 1.39% | 2.98% | |||
Latest Share Price | $ 14.48 | ||||||||||
Latest Premium (Discount) to NAV [Percent] | 0.84% | ||||||||||
Latest NAV | $ 14.36 | ||||||||||
Capital Stock, Long-Term Debt, and Other Securities [Abstract] | |||||||||||
Outstanding Security, Title [Text Block] | Common | ||||||||||
Outstanding Security, Held [Shares] | |||||||||||
Outstanding Security, Not Held [Shares] | 46,810,046 | ||||||||||
Note [Member] | |||||||||||
General Description of Registrant [Abstract] | |||||||||||
Investment Objectives and Practices [Text Block] | Investment Objective The Fund’s investment objective is to provide current income exempt from regular federal income tax, consistent with preservation of capital. The Fund cannot assure you that it will achieve its investment objective. The Fund’s investment objective and any investment policies identified as fundamental may not be changed without shareholder approval. Investment Policies Under normal circumstances and as a fundamental policy, the Fund invests at least 80% of its Managed Assets in municipal securities and other related investments, the income from which is exempt from regular federal income tax and federal alternative minimum tax. Also, under normal circumstances and as a fundamental policy, the Fund may invest up to 20% of its Managed Assets in AMT Bonds. As a non‑fundamental policy, the Fund seeks to achieve its investment objective by investing in a diversified portfolio of municipal securities at least 80% comprised of investment grade quality securities, the income from which is exempt from regular federal income tax. Nuveen Asset Management seeks to identify and invest in municipal securities that it believes are underrated and undervalued, based on a bottom‑up, research-driven investment strategy. Nuveen Asset Management believes its value-oriented strategy offers the opportunity to construct a well-diversified portfolio of municipal securities that has the potential to outperform major municipal market benchmarks over the longer term. Underrated municipal securities are those whose credit ratings do not, in Nuveen Asset Management’s opinion, reflect their true creditworthiness. Undervalued municipal securities are securities that, in Nuveen Asset Management’s opinion, are worth more than the value assigned to them in the marketplace. A municipal security’s market value generally will depend upon its form, maturity, call features and interest rate, as well as the issuer’s credit quality or credit rating, all such factors examined in the context of the municipal securities market and interest rate levels and trends. Nuveen Asset Management may at times believe that securities associated with a particular municipal market sector (for example, electric utilities), or issued by a particular municipal issuer, are undervalued. Nuveen Asset Management may purchase such a security for the Fund’s portfolio because it represents a market sector or issuer that Nuveen Asset Management considers undervalued, even if the value of the particular security appears to be consistent with the value of similar securities. Municipal securities of particular types ( e.g. The Fund may invest in various municipal securities, including municipal bonds and notes, other securities issued to finance and refinance public projects, and other related securities and derivative instruments creating exposure to municipal bonds, notes and securities that provide for the payment of interest income that is exempt from regular federal income tax. Municipal securities are often issued by state and local governmental entities to finance or refinance public projects, such as roads, schools, and water supply systems. Municipal securities also may be issued on behalf of private entities or for private activities, such as housing, medical and educational facility construction, or for privately owned transportation, electric utility or pollution control projects. Municipal securities may be issued on a long-term basis to provide long-term financing. The repayment of such debt may be secured generally by a pledge of the full faith and credit taxing power of the issuer, a limited or special tax, or any other revenue source, including project revenues, which may include tolls, fees and other user charges, lease payments, and mortgage payments. Municipal securities also may be issued to finance projects on a short-term interim basis, anticipating repayment with the proceeds of the later issuance of long-term debt. The Fund may purchase municipal securities in the form of bonds, notes, leases or certificates of participation; structured as callable or non‑callable; with payment forms that include fixed coupon, variable rate or zero coupon, including capital appreciation bonds, floating rate securities, and inverse floating rate securities; or acquired through investments in pooled vehicles, partnerships, or other investment companies. The Fund may invest in these types of securities, including floating rate securities and inverse floating rate securities, in order to more efficiently achieve its desired overall portfolio structure as well as enhance its ability to achieve its investment objective. As a fundamental policy, the Fund will not leverage its capital structure by issuing senior securities such as preferred shares or debt instruments. However, the Fund may borrow for temporary, emergency or other purposes as permitted by the 1940 Act, and invest in certain instruments, including inverse floating rate securities, that have the economic effect of leverage. There can be no assurance that the Fund’s leverage strategy will be successful. The use of leverage creates special risks for Common Shareholders. See “Use of Leverage,” “Risk Factors—Leverage Risk,” and “Risk Factors—Inverse Floating Rate Securities Risk.” The Fund also may invest in derivative instruments in pursuit of its investment objective, including inverse floating rate securities. Such also instruments include financial futures contracts, swap contracts (including interest rate and credit default swaps), options on financial futures, options on swap contracts, or other derivative instruments. However, the Fund may not enter into futures contracts or related options or forward contracts, if more than 30% of the Fund’s net assets would be represented by futures contracts or more than 5% of the Fund’s net assets would be committed to initial margin deposits and premiums on futures contracts and related options. Nuveen Asset Management uses derivatives to seek to enhance return, to hedge some of the risks of its investments in fixed income securities or as a substitute for a position in the underlying asset. These types of hedging strategies may generate taxable income. See “The Fund’s Investments.” As a fundamental policy, the Fund may invest up to 20% of its Managed Assets in AMT Bonds. Any such investment by the Fund will not be counted towards meeting its 80% investment in municipal securities exempt from regular federal income tax and federal alternative minimum tax. For a discussion of how the federal alternative minimum tax may affect shareholders, see “Tax Matters.” Under normal circumstances: • As a non‑fundamental policy, the Fund invests at least 80% of its Managed Assets in municipal securities and other related investments that at the time of investment are investment grade quality. A security is considered investment grade quality if it is rated within the four highest letter grades (BBB or Baa or better) by at least one of the NRSROs that rate such security (even if it is rated lower by another), or if it is unrated by any NRSRO but judged to be of comparable quality by Nuveen Asset Management. • As a non‑fundamental policy, the Fund may invest up to 20% of its Managed Assets in municipal securities that at the time of investment are rated below investment grade or are unrated by any NRSRO but judged to be of comparable quality by Nuveen Asset Management. Also as a non‑fundamental policy, no more than 10% of the Fund’s Managed Assets may be invested in municipal securities rated below B3/B‑ or that are unrated but judged to be of comparable quality by Nuveen Asset Management. Municipal securities of below investment grade quality are regarded as having predominately speculative characteristics with respect to capacity to pay interest and repay principal, and are commonly referred to as junk bonds. See “Risk Factors—Credit and Below Investment Grade Risk.” • The Fund will not invest more than 50% of its Managed Assets in municipal securities that, at the time of investment, are illiquid ( i.e. • As of April 30, 2023, the effective maturity of the Fund’s portfolio was 14.09 years. The Fund is a long-term bond fund and, as such, will generally maintain, under normal market conditions, an investment portfolio with an overall weighted average maturity of greater than 10 years. In comparison to maturity (which is the date on which a debt instrument ceases and the issuer is obligated to repay the principal amount), duration is a measure of the price volatility of a debt instrument as a result of changes in market rates of interest, based on the weighted average timing of the instrument’s expected principal and interest payments. Duration differs from maturity in that it considers a security’s yield, coupon payments, principal payments and call features in addition to the amount of time until the security finally matures. As the value of a security changes over time, so will its duration. Prices of securities with longer durations tend to be more sensitive to interest rate changes than securities with shorter durations. In general, a portfolio of securities with a longer duration can be expected to be more sensitive to interest rate changes than a portfolio with a shorter duration. For example, the price of a bond with an effective duration of two years will rise (fall) two percent for every one percent decrease (increase) in its yield, and the price of a five-year duration bond will rise (fall) five percent for a one percent decrease (increase) in its yield. As of April 30, 2023, the average effective duration of the Fund’s portfolio was 7.32 years, which includes the effects of leverage and takes into account the effect of option call provisions of the municipal securities in the Fund’s portfolio. • The Fund will not invest more than 25% of its Managed Assets in municipal securities in any one industry or in any one state of origin and no more than 5% of its Managed Assets in any one issuer. Any non‑fundamental policy of the Fund may be changed by the Fund’s Board following the provision of 60 days prior written notice to Common Shareholders. The foregoing credit quality policies apply only at the time a security is purchased, and the Fund is not required to dispose of a security in the event that an NRSRO downgrades its assessment of the credit characteristics of a particular issuer or that valuation changes of various bonds cause the Fund’s portfolio to fail to satisfy those policies. In determining whether to retain or sell such a security, Nuveen Asset Management may consider such factors as Nuveen Asset Management’s assessment of the credit quality of the issuer of such security, the price at which such security could be sold and the rating, if any, assigned to such security by other rating agencies. A general description of the ratings of municipal securities of S&P, Moody’s and Fitch is set forth in Appendix A to the SAI. The Fund may purchase municipal securities that are additionally secured by insurance, bank credit agreements or escrow accounts. The credit quality of companies which provide such credit enhancements may affect the value of those securities. Although the insurance feature may reduce certain financial risks, the premiums for insurance and the higher market price paid for insured obligations may reduce the Fund’s income. The Fund may use any insurer, regardless of its rating. A municipal security typically will be deemed to have the rating of its insurer. However, in the event an insurer has a credit rating below the rating of an underlying municipal security or is perceived by the market to have such a lower rating, the municipal security rating would be the more relevant rating and the value of the municipal security would more closely, if not entirely, reflect such rating. As a result, the value of insurance associated with a municipal security may decline and the insurance may not add any value. The insurance feature normally provides that it guarantees the full payment of principal and interest when due of an insured obligation, but does not guarantee the market value of the insured obligation or the net asset value of the Common Shares represented by such insured obligation. See “Risk Factors—Insurance Risk.” During temporary defensive periods or in order to keep the Fund’s cash fully invested, including during the period when the net proceeds of the offering of Common Shares are being invested, the Fund may deviate from its investment policies and objectives. During such periods, the Fund may invest up to 100% of its Managed Assets in short-term investments, including high quality, short-term securities that may be either tax‑exempt or taxable (or in securities of other open- or closed‑end investment companies that invest primarily in municipal securities of the types in which the Fund may invest directly). The Fund may not achieve its investment objective during such period. The Fund intends to invest in taxable short-term investments only in the event that suitable tax‑exempt short-term investments are not available at reasonable prices and yields. Investment in taxable short-term investments would result in a portion of your dividends being subject to regular federal income tax, and if the proportion of taxable investments exceeded 50% of the Fund’s total assets as of the close of any quarter of the Fund’s taxable year, the Fund would not satisfy the general eligibility test that permits it to pay exempt-interest dividends. Such transactions will be used solely to reduce risk. There can be no assurance that such strategies will be successful. For more information, see the SAI under “Tax Matters.” The Fund’s investment objective and certain investment policies specifically identified as such are considered fundamental and may not be changed without shareholder approval. See “Investment Restrictions” in the SAI. All of the Fund’s other investment policies are not considered to be fundamental by the Fund and can be changed by the Fund’s Board without a vote of the Common Shareholders. The Fund cannot change its investment objective or fundamental policies without the approval of the holders of a “majority of the outstanding” Common Shares. When used with respect to particular shares of the Fund, a “majority of the outstanding” shares means (i) 67% or more of the shares present at a meeting, if the holders of more than 50% of the shares are present or represented by proxy, or (ii) more than 50% of the shares, whichever is less. If you are, or as a result of investment in the Fund would become, subject to the federal alternative minimum tax, the Fund may not be a suitable investment for you because the Fund may invest up to 20% of its Managed Assets in municipal securities that will pay interest that is taxable under the federal alternative minimum tax. Special rules apply to corporate holders. In addition, distributions of net capital gain will be taxable as long-term capital gains taxes. See “Tax Matters.” | ||||||||||
[1]You will be charged a $2.50 service charge and pay brokerage charges if you direct State Street Bank and Trust Company, as agent for the Common Shareholders (the “Plan Agent”), to sell your Common Shares held in a dividend reinvestment account.[2]Stated as annualized percentages of average net assets attributable to Common Shares for the fiscal year ended March 31, 2023.[3]Interest and Related Expenses from Inverse Floaters also includes interest expense that arises because accounting rules require the Fund to treat interest paid by trusts issuing certain inverse floating rate investments held by the Fund as having been paid (indirectly) by the Fund. Because the Fund also recognizes a corresponding amount of interest income (also indirectly), the Fund’s net asset value, net investment income, and total return are not affected by this accounting treatment. The actual Interest and Related Expenses from Inverse Floaters incurred in the future may be higher or lower.[4]Assuming a Common Share offering price of $14.48 (the Fund’s closing price on the NYSE on May 31, 2023).[5]Other Expenses is based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%. See “Investment Policies and Techniques—Other Investment Companies” in the SAI. |