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N-2 - USD ($) | Jul. 31, 2023 | May 31, 2023 | Feb. 28, 2023 | Nov. 30, 2022 | Aug. 31, 2022 | May 31, 2022 | Feb. 28, 2022 | Nov. 30, 2021 | Aug. 31, 2021 | May 31, 2021 | [5]
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Cover [Abstract] |  |  |  |  |  |  |  |  |  |  |
Entity Central Index Key |  | 0000885732 |  |  |  |  |  |  |  |  |
Amendment Flag |  | false |  |  |  |  |  |  |  |  |
Entity Inv Company Type |  | N-2 |  |  |  |  |  |  |  |  |
Securities Act File Number |  | 333-271871 |  |  |  |  |  |  |  |  |
Investment Company Act File Number |  | 811-06623 |  |  |  |  |  |  |  |  |
Document Type |  | N-2/A |  |  |  |  |  |  |  |  |
Document Registration Statement |  | true |  |  |  |  |  |  |  |  |
Pre-Effective Amendment |  | true |  |  |  |  |  |  |  |  |
Pre-Effective Amendment Number |  | 1 |  |  |  |  |  |  |  |  |
Post-Effective Amendment |  | false |  |  |  |  |  |  |  |  |
Investment Company Act Registration |  | true |  |  |  |  |  |  |  |  |
Investment Company Registration Amendment |  | true |  |  |  |  |  |  |  |  |
Investment Company Registration Amendment Number |  | 6 |  |  |  |  |  |  |  |  |
Entity Registrant Name |  | Nuveen California Select Tax‑Free Income Portfolio |  |  |  |  |  |  |  |  |
Entity Address, Address Line One |  | 333 West Wacker Drive |  |  |  |  |  |  |  |  |
Entity Address, City or Town |  | Chicago |  |  |  |  |  |  |  |  |
Entity Address, State or Province |  | IL |  |  |  |  |  |  |  |  |
Entity Address, Postal Zip Code |  | 60606 |  |  |  |  |  |  |  |  |
City Area Code |  | 800 |  |  |  |  |  |  |  |  |
Local Phone Number |  | 257‑8787 |  |  |  |  |  |  |  |  |
Approximate Date of Commencement of Proposed Sale to Public |  | As soon as practicable after the effective date of this Registration Statement. |  |  |  |  |  |  |  |  |
Dividend or Interest Reinvestment Plan Only |  | false |  |  |  |  |  |  |  |  |
Delayed or Continuous Offering |  | true |  |  |  |  |  |  |  |  |
Primary Shelf [Flag] |  | true |  |  |  |  |  |  |  |  |
Effective Upon Filing, 462(e) |  | false |  |  |  |  |  |  |  |  |
Additional Securities Effective, 413(b) |  | false |  |  |  |  |  |  |  |  |
Effective when Declared, Section 8(c) |  | false |  |  |  |  |  |  |  |  |
New Effective Date for Previous Filing |  | false |  |  |  |  |  |  |  |  |
Additional Securities. 462(b) |  | false |  |  |  |  |  |  |  |  |
No Substantive Changes, 462(c) |  | false |  |  |  |  |  |  |  |  |
Exhibits Only, 462(d) |  | false |  |  |  |  |  |  |  |  |
Registered Closed-End Fund [Flag] |  | true |  |  |  |  |  |  |  |  |
Business Development Company [Flag] |  | false |  |  |  |  |  |  |  |  |
Interval Fund [Flag] |  | false |  |  |  |  |  |  |  |  |
Primary Shelf Qualified [Flag] |  | true |  |  |  |  |  |  |  |  |
Entity Well-known Seasoned Issuer |  | No |  |  |  |  |  |  |  |  |
Entity Emerging Growth Company |  | false |  |  |  |  |  |  |  |  |
New CEF or BDC Registrant [Flag] |  | false |  |  |  |  |  |  |  |  |
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(1) |  |  | 0.78 | %
Dividend Reinvestment Plan Fees(2) |  |  | $2.50 |
|  | As a Percentage of Net Assets Attributable to Common Shares(3) |
Annual Expenses |  |  |  |
Management Fees |  |  | 0.26 | %
Other Expenses(4) |  |  | 0.10 | %
Total Annual Expenses |  |  | 0.36 | %
(1) | Assuming a Common Share offering price of $13.35 (the Fund’s closing price on the NYSE on July 18, 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] |  | 1.00% |  |  |  |  |  |  |  |  |
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(1) |  |  | 0.78 | %
Dividend Reinvestment Plan Fees(2) |  |  | $2.50 |
|  | As a Percentage of Net Assets Attributable to Common Shares(3) |
Annual Expenses |  |  |  |
Management Fees |  |  | 0.26 | %
Other Expenses(4) |  |  | 0.10 | %
Total Annual Expenses |  |  | 0.36 | %
(3) | Stated as annualized percentages of average net assets attributable to Common Shares for the fiscal year ended February 28, 2023.
(4) | 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 “Portfolio Composition—Other Investment Companies” in the SAI.
Management Fees [Percent] | [2] | 0.26% |  |  |  |  |  |  |  |  |
Distribution/Servicing Fees [Percent] | [3] | 0.78% |  |  |  |  |  |  |  |  |
Other Annual Expenses [Abstract] |  |  |  |  |  |  |  |  |  |  |
Other Annual Expenses [Percent] | [2],[4] | 0.10% |  |  |  |  |  |  |  |  |
Total Annual Expenses [Percent] | [2] | 0.36% |  |  |  |  |  |  |  |  |
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 $7.80 that a Common 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 |
$21 |  |  | $29 |  |  |  | $38 |  |  |  | $63 |
(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 |  | $ 21 |  |  |  |  |  |  |  |  |
Expense Example, Years 1 to 3 |  | 29 |  |  |  |  |  |  |  |  |
Expense Example, Years 1 to 5 |  | 38 |  |  |  |  |  |  |  |  |
Expense Example, Years 1 to 10 |  | $ 63 |  |  |  |  |  |  |  |  |
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 total investment exposure. |  |  |  |  |  |  |  |  |
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 “Portfolio Composition—Other Investment Companies” in the SAI. |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Investment Objectives and Practices [Text Block] |  | Investment Objective The Fund’s investment objective is to provide stable dividends exempt from both regular federal and California income taxes, 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 will invest at least 80% of its Managed Assets, plus the amount of any borrowings for investment purposes, in municipal securities, the income from which is exempt from regular federal and California income taxes. The Fund may invest up to 20% of its Managed Assets in AMT Bonds. The Fund will consider its investment in underlying investment companies when determining its compliance with its policy to invest at least 80% of its Managed Assets, plus the amount of any borrowings for investment purposes, in municipal securities, the income from which is exempt from regular federal income tax. The Fund seeks to achieve its investment objective by investing in a portfolio of California municipal securities, a significant portion of which Nuveen Asset Management believes are underrated and undervalued, based upon its bottom‑up, research-driven investment strategy. Underrated municipal securities are those whose 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. Nuveen Asset Management employs a value-oriented strategy and seeks to construct a diversified portfolio of municipal securities that has the potential to outperform major municipal market benchmarks over the longer term. 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., hospital bonds, industrial revenue bonds or securities issued by a particular municipal issuer) may be undervalued because there is a temporary excess of supply in that market sector, or because of a general decline in the market price of municipal securities of the market sector for reasons that do not apply to the particular municipal securities that are considered undervalued. The Fund’s investment in underrated or undervalued municipal securities will be based on Nuveen Asset Management’s belief that the prices of such municipal securities should ultimately reflect their true value. The Fund may invest up to 15% of its Managed Assets in inverse floating rate securities. There can be no assurance that the Fund will achieve its investment objective. 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 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, tender option bonds, and inverse floating rate securities; or acquired through investments in pooled vehicles, partnerships, or other investment companies. The Fund also may invest in certain derivative instruments in pursuit of its investment objective. Such 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. Nuveen Asset Management may use derivative instruments to seek to enhance return, to hedge some of the risk of the Fund’s investments in municipal securities or as a substitute for a position in the underlying asset. These types of hedging strategies may generate taxable income. With respect to the Fund’s policy to invest at least 80% of its Managed Assets (plus any borrowings for investment purposes) in municipal securities and other related investments, the income from which is exempt from regular federal and California income taxes, for purposes of calculating Managed Assets, the Fund will value eligible derivatives at market value or fair value instead of notional value. As of June 30, 2023, the Fund was not invested in derivatives. See “The Fund’s Investments—Municipal Securities Derivatives.” Under normal circumstances:
| • |  | The Fund will invest at least 80% of its Managed Asset in investment grade securities that, at the time of investment, are rated within the four highest grades (Baa or BBB or better) by at least one NRSRO or are unrated but judged to be of comparable quality by Nuveen Asset Management. A security is considered investment grade if it is rated within the four highest letter grades by at least one NRSRO that rate such securities (even if rated lower by another), or if it is unrated but judged to be of comparable quality by Nuveen Asset Management.
As of June 30, 2023, approximately 84% of the Fund’s total investment exposure were invested in municipal securities rated investment grade by an NRSRO (including Standard & Poor’s Corporation Ratings Group, a division of The McGraw-Hill Companies (“S&P”), Moody’s Investors Services, Inc. (“Moody’s”) or 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.
| • |  | The Fund may invest up to 20% of its Managed in municipal securities that at the time of investment are rated below investment grade or are unrated but judged to be of comparable quality by Nuveen Asset Management. No more than 10% of the Fund’s Managed Assets may be invested in municipal securities rated below B3/B‑ by all NRSROs that rate the security 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 predominantly speculative characteristics with respect to capacity to pay interest and repay principal, and are commonly referred to as junk bonds. The Fund may invest in distressed
| securities. The Fund may not invest in the securities of an issuer which, at the time of investment, is in default on its obligations to pay principal or interest thereon when due or that is involved in a bankruptcy proceeding (i.e., rated below C‑, at the time of investment); provided, however, that Nuveen Asset Management may determine that it is in the best interest of shareholders in pursuing a workout arrangement with issuers of defaulted securities to make loans to the defaulted issuer or another party, or purchase a debt, equity or other interest from the defaulted issuer or another party, or take other related or similar steps involving the investment of additional monies, but only if that issuer’s securities are already held by the Fund.
| • |  | 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 financial leverage.
| • |  | The Fund may invest up to 15% of its Managed Assets in inverse floating rate securities.
| • |  | The Fund may invest up to 10% of its net assets in securities of other open- or closed‑end investment companies that invest primarily in municipal bonds of the types in which the Fund may invest directly.
| • |  | The Fund may invest in municipal securities and other instruments that, at the time of investment, are illiquid (i.e., securities that are not readily marketable). See “Risk Factors—Illiquid Securities Risk.”
| • |  | The Fund will not invest more than 25% of its total assets in municipal securities in any one industry.
For purposes of the Fund’s investment policies, “Managed Assets” mean 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. The credit quality policies noted above apply only at the time a security is purchased, and the Fund is not required to dispose of a security in the event that a rating agency downgrades its assessment of the credit characteristics of a particular issue, even if such downgrade causes the portfolio to fall below the 80% threshold. If at any time the Fund falls below the 80% threshold, the Fund’s future investments will be made in a manner that will bring the Fund’s portfolio back into compliance with this policy. 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 S&P, Moody’s and Fitch of municipal securities 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 that provide such credit enhancements will affect the value of those securities. Although the insurance feature is designed to 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 may not add any value. The insurance feature does not guarantee the full payment of principal and interest of an insured obligation, the market value of the insured obligation or the net asset value of the Common Shares represented by such insured obligation. 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 net 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 more information, see the SAI under “Tax Matters.” The Fund cannot change its investment objective or fundamental policies without the approval of the holders of a “majority of the outstanding” Common Shares. For this purpose, 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. 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. As discussed in greater detail under “Investment Restrictions” in the SAI, the Fund as a fundamental policy, may not, without the approval of the holders of a majority of the outstanding Shares:
| (1) | Issue senior securities as defined in the 1940 Act, except to the extent such issuance might be involved with respect to borrowings described under subparagraph (2) below.
| (2) | Borrow money, except as permitted by the 1940 Act and exemptive orders granted under the 1940 Act.
| (3) | Act as underwriter of another issuer’s securities, except to the extent that the Fund may be deemed to be an underwriter within the meaning of the Securities Act of 1933 (the “1933” Act) in connection with the purchase and sale of portfolio securities.
| (4) | Invest more than 25% of its total assets in securities of issuers in any one industry; provided, however, that such limitation shall not be applicable to municipal securities other than those municipal securities backed only by the assets and revenues of non-governmental users, nor shall it apply to municipal securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities.
| (5) | Purchase or sell real estate, but this shall not prevent the Fund from investing in municipal securities secured by real estate or interests therein or foreclosing upon and selling such security.
| (6) | Purchase or sell physical commodities unless acquired as a result of ownership of securities or other instruments (but this shall not prevent the Fund from purchasing or selling options, futures contracts, derivative instruments or from investing in securities or other instruments backed by physical commodities).
| (7) | Make loans, except as permitted by the 1940 Act and exemptive orders granted under the 1940 Act.
| (8) | With respect to 75% of the value of the Fund’s total assets, purchase any securities (other than obligations issued or guaranteed by the United States government or by its agencies or instrumentalities, and securities issued by other investment companies), if as a result more than 5% of the Fund’s total assets would then be invested in securities of a single issuer or if as a result the Fund would hold more than 10% of the outstanding voting securities of any single issuer.
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 amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the investment performance of the Fund may therefore be more dependent on the analytical abilities of Nuveen Asset Management than if the Fund were a stock fund or taxable bond fund. The secondary market for municipal securities, particularly the below investment grade bonds in which the Fund may invest, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices. In addition, the market for below investment grade municipal securities has experienced in the past, and may experience in the future, periods of significant volatility, which could negatively impact the value of the municipal securities in the Fund’s portfolio and the market price of the Common Shares. 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. Issuers of securities in which the Fund may invest may default on their obligations to pay principal or interest when due. This non‑payment would result in a reduction of income to the Fund, a reduction in the value of a debt security experiencing non‑payment and, potentially, a decrease in the NAV of the Fund. With respect to the Fund’s investments in securities that are secured, there can be no assurance that liquidation of collateral would satisfy the issuer’s obligation in the event of non‑payment of a scheduled interest or principal payment or that such collateral could be readily liquidated. In the event of the bankruptcy of an issuer the Fund could experience delays or limitations with respect to its ability to realize the benefits of any collateral securing a security. To the extent that the credit rating assigned to a security in the Fund’s portfolio is downgraded, the market price and liquidity of such security may be adversely affected. Credit Spread Risk. Credit spread risk is the risk that credit spreads (i.e., the difference in yield between securities that is due to differences in their credit quality) may increase when the market believes that municipal securities generally have a greater risk of default. Increasing credit spreads may reduce the market values of the Fund’s securities. Credit spreads often increase more for lower rated and unrated securities than for investment grade securities. In addition, when credit spreads increase, reductions in market value will generally be greater for longer-maturity securities. Below Investment Grade Risk. Debt instruments of below investment grade quality are regarded as having predominately speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal, and are commonly referred to as junk bonds or high yield debt, which implies higher price volatility and default risk than investment grade instruments of comparable terms and duration. Issuers of lower grade instruments may be highly leveraged and may not have available to them more traditional methods of financing. The prices of these lower grade instruments are typically more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn, than are the prices of higher grade instruments. 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. Interest rate risk is the risk that debt securities in the Fund’s portfolio will decline in value because of changes in market interest rates. Generally, when market interest rates rise, the market value of such securities will fall, and vice versa. As interest rates decline, issuers of debt securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower-yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower than expected principal payments may extend the average life of securities, potentially locking in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer-term debt securities generally fluctuate more than prices of shorter-term debt securities as interest rates change. As of the date of this Prospectus, the risk of rising interest rates may be greater than would normally be the case due to the current changes in government fiscal policy initiatives and resulting market reaction to those initiatives. Because the market price of debt securities may change based upon investors’ collective perceptions of future earnings, the value of the Fund will generally decline when investors anticipate or experience rising interest rates. London Inter-bank Offered Rate (“LIBOR”) Transition Risk. To the extent that a debt security continues to use LIBOR as a benchmark or reference rate for interest rate calculations, such security is subject to risks related to the transition from LIBOR to the Secured Overnight Funding Rate (“SOFR”). SOFR has been selected by a committee established by the Board of Governors of the Federal Reserve System and the Federal Reserve Bank of New York to replace LIBOR as a reference rate for certain financial contracts in the United States after June 30, 2023. However, there remains uncertainty regarding the new replacement rate as well as the impact of the transition from LIBOR on the Fund and the financial markets generally. Other countries have undertaken similar initiatives to identify replacement reference rates in their respective markets. The transition process, or the failure of an industry to transition, could lead to increased volatility and illiquidity in markets for instruments that currently rely on LIBOR to determine interest rates, and a reduction in the values of some LIBOR-based investments, all of which could impact the Fund. Duration Risk. Duration is the sensitivity, expressed in years, of the price of a fixed-income security to changes in the general level of interest rates (or yields). Securities with longer durations tend to be more sensitive to interest rate (or yield) changes, which typically corresponds to increased volatility and risk, than securities with shorter durations. For example, if a security or portfolio has a duration of three years and interest rates increase by 1%, then the security or portfolio would decline in value by approximately 3%. Duration differs from maturity in that it considers potential changes to interest rates, and a security’s coupon payments, yield, price and par value and call features, in addition to the amount of time until the security matures. The duration of a security will be expected to change over time with changes in market factors and time to maturity. Call Risk. The Fund may invest in debt securities that are subject to call risk. Such municipal securities may be redeemed at the option of the issuer, or “called,” before their stated maturity or redemption date. In general, an issuer will call its instruments if they can be refinanced by issuing new instruments which bear a lower interest rate. The Fund is subject to the possibility that during periods of falling interest rates, an issuer will call its high yielding municipal securities. The Fund would then be forced to invest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund’s income. Prepayment Risk. Prepayment risk is the risk that the issuer of a debt security will repay principal (in part or in whole) prior to the scheduled maturity date. Debt securities allowing prepayment may offer less potential for gains during a period of declining interest rates, as the Fund may be required to reinvest the proceeds of any prepayment at lower interest rates, reducing its income. If the Fund purchased the debt securities at a premium, prepayments on the securities could cause the Fund to lose a portion of its principal investment. These factors may cause the value of an investment in the Fund to change. The impact of prepayments on the price of a debt security may be difficult to predict and may increase the security’s volatility. Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called securities at market interest rates that are below the portfolio’s current earnings rate. A decline in income could affect the Common Shares’ market price, NAV and/or a Common Shareholder’s overall returns. Alternative Minimum Tax Risk. The Fund may invest in AMT Bonds. Therefore, a portion of the Fund’s otherwise exempt-interest dividends may be taxable to those shareholders subject to the federal alternative minimum tax. Inverse Floating Rate Securities Risk. The Fund may invest in inverse floating rate securities. Typically, inverse floating rate securities represent beneficial interests in a special purpose trust (sometimes called a “tender option bond trust”) formed for the purpose of holding municipal bonds. See “The Fund’s Investments—Portfolio Composition—Municipal Securities—Inverse Floating Rate Securities.” In general, income on inverse floating rate securities will decrease when short-term interest rates increase and increase when short-term interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal. 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. Inventories of municipal securities held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell municipal securities at attractive prices, and increase municipal security price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. The secondary market for municipal securities, particularly the below investment grade municipal securities in which the Fund may invest, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of municipal securities to raise cash to meet its obligations, those sales could further reduce the municipal securities’ prices and hurt performance. The Fund may invest a significant portion of its assets in unrated municipal securities. The market for these municipal securities may be less liquid than the market for rated municipal securities of comparable quality. Less public information is typically available about unrated municipal securities or issuers than rated municipal securities or issuers. Special Risks Related to Certain Municipal Obligations. Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non‑appropriation” clauses that relieve the governmental issuer of any obligation to make future payments under the lease or contract unless money is appropriated for such purpose by the appropriate legislative body. In addition, such leases or contracts may be subject to the temporary abatement of payments in the event that the governmental issuer is prevented from maintaining occupancy of the leased premises or utilizing the leased equipment. Although the obligations may be secured by the leased equipment or facilities, the disposition of the property in the event of non‑appropriation or foreclosure might prove difficult, time consuming and costly, and may result in a delay in recovering or the failure to fully recover the Fund’s original investment. In the event of non‑appropriation, the issuer would be in default and taking ownership of the assets may be a remedy available to the Fund, although the Fund does not anticipate that such a remedy would normally be pursued. To the extent that the Fund invests in unrated municipal leases or participates in such leases, the credit quality rating and risk of cancellation of such unrated leases will be monitored on an ongoing basis. 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. Illiquid investments are securities that are not readily marketable. These securities may include restricted securities, which cannot be resold to the public without an effective registration statement under the 1933 Act, or, if they are unregistered, may be 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. The Fund may invest in low‑rated securities or securities unrated but judged by the sub‑adviser to be of comparable quality. Some or many of these low‑rated securities, although not in default, may be “distressed,” meaning that the issuer is experiencing financial difficulties or distress at the time of acquisition. Such securities would present a substantial risk of future default which may cause the Fund to incur losses, including additional expenses, to the extent it is required to seek recovery upon a default in the payment of principal or interest on those securities. In any reorganization or liquidation proceeding relating to a portfolio security, the Fund may lose its entire investment or may be required to accept cash or securities with a value less than its original investment. Distressed securities may be subject to restrictions on resale. Derivatives Risk. The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a municipal security or other asset without buying or selling the municipal security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over‑the‑counter derivative transaction between the Fund and a counterparty that is not cleared through a central counterparty also involves the risk that a loss may be sustained as a result of the failure of the counterparty to the contract to make required payments. The payment obligation for a cleared derivative transaction is guaranteed by a central counterparty, which exposes the Fund to the creditworthiness of the central counterparty. It is possible that developments in the derivatives market, including changes in government regulation, could adversely impact the Fund’s ability to invest in certain derivatives. 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 may enter into debt-related derivatives instruments such as credit default swap contracts and interest rate swaps. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by Nuveen Asset Management not only of the referenced asset, rate or index, but also of the swap itself. If Nuveen Fund Advisors and/or Nuveen Asset Management is incorrect in its forecasts of default risks, market spreads or other applicable factors or events, the investment performance of the Fund would diminish compared with what it would have been if these techniques were not used. As the protection seller in a credit default swap, the Fund effectively adds leverage to its portfolio because, in addition to being subject to investment exposure on its total net assets, the Fund is subject to investment exposure on the notional amount of the swap. 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. The Fund may use certain transactions for hedging the portfolio’s exposure to credit risk and the risk of increases in interest rates, which could result in poorer overall performance for the Fund. The Fund’s use of certain transactions to reduce risk involves costs and will be subject to Nuveen Asset Management’s ability to predict correctly changes in the relationships of such hedge 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. 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 Commodity Futures Trading Commission (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. The Fund’s use of derivatives or other transactions to reduce risks involves costs and will be subject to Nuveen Asset Management’s ability to predict correctly changes in the relationships of such hedge 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. Concentration Risk in California Issuers. The Fund’s policy of investing in municipal securities of issuers located in California makes the Fund more susceptible to the adverse economic, political or regulatory occurrences affecting such issuers. The information set forth below and the related information in Appendix A of this Prospectus is derived from sources that are generally available to investors. The information is intended to give a recent historical description and is not intended to indicate future or continuing trends in the financial or other positions of California. It should be noted that the creditworthiness of obligations issued by local California issuers may be unrelated to the creditworthiness of obligations issued by the State of California, and that there is no obligation on the part of the State to make payment on such local obligations in the event of default. California is subject to large fluctuations in its tax revenue and fixed spending obligations. During recessionary periods, which California recently experienced, dramatic cuts to programs and/or tax increases may be required. To address budget gaps from the recent recessionary period, spending was cut, State programs were realigned to local governments, and short-term budgetary solutions were implemented. Despite the recent significant budgetary improvements and moderate growth, a number of major risks and pressures threaten the State’s financial condition, including the need to repay billions of dollars of obligations that were deferred to balance budgets during the economic downturn. Continued risks to the State’s long-term stability include pension liabilities, debt and increasing annual obligations, and potential cost increases associated with the federal deficit. California’s fiscal situation heightens the risk of investing in bonds issued by the State and its political subdivisions, agencies, instrumentalities and authorities, including the risk of default, and also heightens the risk that the prices of California municipal securities, and the Fund’s net asset value, will experience greater volatility. As of June 30, 2023, California general obligation bonds were rated “Aa2” by Moody’s, “AA‑” with Positive Outlook by S&P and “AA” by Fitch. There can be no assurance that such ratings will be maintained in the future. The State’s credit rating, and any future revisions or withdrawal of a credit rating, could have a negative effect on the market price of the State’s general obligation bonds, as well as notes and bonds issued by California’s public authorities and local governments. Lower credit ratings make it more expensive for the State to raise revenue, and in some cases, could prevent the State from issuing general obligation bonds in the quantity otherwise desired. Further, downgrades can negatively impact the marketability and price of securities in the Fund’s portfolio. The foregoing information constitutes only a brief summary of some of the general factors that may impact certain issuers of municipal bonds and does not purport to be a complete or exhaustive description of all adverse conditions to which the issuers of municipal bonds held by the Fund are subject. Additionally, many factors, including national economic, social and environmental policies and conditions, which are not within the control of the issuers of the municipal bonds, could affect or could have an adverse impact on the financial condition of the issuers. The Fund is unable to predict whether or to what extent such factors or other factors may affect the issuers of the municipal securities, the market value or marketability of the municipal securities or the ability of the respective issuers of the municipal bonds acquired by the Fund to pay interest on or principal of the municipal securities. This information has not been independently verified. See Appendix A of this Prospectus for a further discussion of factors affecting municipal securities in California. Puerto Rico Municipal Securities Market Risk. To the extent that the Fund invests a significant portion of its assets in the securities issued by the Commonwealth of Puerto Rico or its political subdivisions, agencies, instrumentalities, or public corporations (collectively referred to in this Prospectus as “Puerto Rico” or the “Commonwealth”), it will be disproportionally affected by political, social and economic conditions and developments in the Commonwealth. In addition, economic, political or regulatory changes in that territory could adversely affect the value of the Fund’s investment portfolio. 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. At times, the Fund may focus its investments (i.e., overweight its investments relative to the overall municipal securities market) in one or more particular sectors, which may subject the Fund to additional risk and variability. Securities issued in the same sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. As the percentage of the Fund’s Managed Assets invested in a particular sector increases, so does the potential for fluctuation in the NAV of the Common Shares. Sector and Industry Risk. Subject to the concentration limits of the Fund’s investment policies and guidelines, the Fund may invest a significant portion of its net assets in certain sectors of the municipal securities market, such as hospitals and other health care facilities, charter schools and other private educational facilities, special taxing districts and start‑up utility districts, and private activity bonds including industrial development bonds on behalf of transportation companies such as airline companies, whose credit quality and performance may be more susceptible to economic, business, political, regulatory and other developments than other sectors of municipal issuers. If the Fund invests a significant portion of its net assets in the sectors noted above, the Fund’s performance may be subject to additional risk and variability. Economic Sector Risk. The Fund may invest a significant amount of its total assets in municipal securities in the same economic sector. This may make the Fund more susceptible to adverse economic, political or regulatory occurrences affecting an economic sector. As concentration increases, so does the potential for fluctuation in the value of the Fund’s assets. In addition, the Fund may invest a significant portion of its assets in certain sectors of the municipal securities market, such as hospitals and other health care facilities, charter schools and other private educational facilities, special taxing districts and start‑up utility districts, and private activity bonds including industrial development bonds on behalf of transportation companies such as airline companies, whose credit quality and performance may be more susceptible to economic, business, political, regulatory and other developments than other sectors of municipal issuers. If the Fund invests a significant portion of its assets in the sectors noted above, the Fund’s performance may be subject to additional risk and variability. 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. The Fund’s income is based primarily on the interest it earns from its investments, which can vary widely over the short and long term. The Fund’s income could decline due to falling market interest rates. This is because, in a falling interest rate environment, the Fund generally will have to invest the proceeds from maturing portfolio securities in lower-yielding securities. This risk is magnified when prevailing short-term interest rates increase and the Fund holds residual interest municipal bonds. Inflation Risk. Inflation is the reduction in the purchasing power of money resulting from the increase in the price of goods and services. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the Common Shares and distributions can decline. Deflation Risk. Deflation risk is the risk that prices throughout the economy decline over time, which may have an adverse effect on the market valuation of companies, their assets and revenues. In addition, deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. Zero Coupon Bonds Risk. Because interest on zero coupon bonds is not paid on a current basis, the values of zero coupon bonds will be more volatile in response to interest rate changes than the values of bonds that distribute income regularly. Although zero coupon bonds generate income for accounting purposes, they do not produce cash flow, and thus the Fund could be forced to liquidate securities at an inopportune time in order to generate cash to distribute to shareholders as required by tax laws. Tax Risk. To qualify for the favorable U.S. federal income tax treatment generally accorded to a RIC under Subchapter M of the Code the Fund must, among other requirements, derive in each taxable year at least 90% of its gross income from certain prescribed sources and satisfy a diversification test on a quarterly basis. If the Fund fails to satisfy the qualifying income or diversification requirements in any taxable year, the Fund may be eligible for relief provisions if the failures are due to reasonable cause and not willful neglect and if a penalty tax is paid with respect to each failure to satisfy the applicable requirements. Additionally, relief is provided for certain de minimis failures of the diversification requirements where the Fund corrects the failure within a specified period. In order to be eligible for the relief provisions with respect to a failure to meet the diversification requirements, the Fund may be required to dispose of certain assets. If these relief provisions were not available to the Fund and it were to fail to qualify for treatment as a RIC for a taxable year, all of its taxable income (including its net capital gain) would be subject to tax at the 21% regular corporate rate without any deduction for distributions to shareholders, and such distributions would be taxable as ordinary dividends to the extent of the Fund’s current and accumulated earnings and profits. 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 is not 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. The Fund will invest in municipal securities in reliance at the time of purchase on an opinion of bond counsel to the issuer that the interest paid on those securities will be excludable from gross income for regular federal income tax purposes, and neither Nuveen Asset Management nor any other person will independently verify that opinion. Subsequent to the Fund’s acquisition of such a municipal security, however, the security may be determined to pay, or to have paid, taxable income. Distributions of taxable ordinary taxable 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. See “Tax Matters.” Insurance Risk. The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub‑prime mortgages and other lower credit quality investments that have experienced defaults or otherwise suffered extreme credit deterioration. As a result, such losses have reduced the insurers’ capital and called into question their continued ability to perform their obligations under such insurance if they are called upon to do so in the future. While an insured municipal security will typically be deemed to have the rating of its insurer, if the insurer of a municipal security suffers a downgrade in its credit rating or the market discounts the value of the insurance provided by the insurer, the rating of the underlying municipal security will be more relevant and the value of the municipal security would more closely, if not entirely, reflect such rating. In such a case, the value of insurance associated with a municipal security would decline and may not add any value. The insurance feature of a municipal security does not guarantee the full payment of principal and interest through the life of an insured obligation, the market value of the insured obligation or the NAV represented by such insured obligation. Tobacco Settlement Bond Risk. Tobacco settlement bonds are municipal securities that are backed solely by expected revenues to be derived from lawsuits involving tobacco related deaths and illnesses which were settled between certain states and American tobacco companies. Tobacco settlement bonds are secured by an issuing state’s proportionate share in the Master Settlement Agreement (“MSA”). The MSA is an agreement reached out of court in November 1998 between 46 states and nearly all of the U.S. tobacco manufacturers. Under the terms of the MSA, the actual amount of future settlement payments by tobacco manufacturers is dependent on many factors, including, but not limited to, annual domestic cigarette shipments, reduced cigarette consumption, increased taxes on cigarettes, inflation, financial capability of tobacco companies, continuing litigation and the possibility of tobacco manufacturer bankruptcy. Payments made by tobacco manufacturers could be negatively impacted if the decrease in tobacco consumption is significantly greater than the forecasted decline. Valuation Risk. The municipal securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including readily available market quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to sell a portfolio security at the price established by the pricing service, which could result in a loss to the Fund. Pricing services generally price municipal securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Different pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s NAV. Other Investment Companies Risk. The Fund may invest in the securities of other investment companies, including ETFs. Investing in an investment company exposes the Fund to all of the risks of that investment company’s investments. The Fund, as a holder of the securities of other investment companies, will bear its pro rata portion of the other investment companies’ expenses, including advisory fees. These expenses are in addition to the direct expenses of the Fund’s own operations. As a result, the cost of investing in investment company 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. Shares of closed‑end investment companies like the Fund frequently trade at prices lower than their NAV. This characteristic is a risk separate and distinct from the risk that the Fund’s NAV could decrease as a result of investment activities. Whether investors will realize gains or losses upon the sale of the Common Shares will depend not upon the Fund’s NAV but entirely upon whether the market price of the Common Shares at the time of sale is above or below the investor’s purchase price for the Common Shares. Furthermore, management may have difficulty meeting the Fund’s investment objectives and managing its portfolio when the underlying securities are redeemed or sold during periods of market turmoil and as investors’ perceptions regarding closed‑end funds or their underlying investments change. Because the market price of the Common Shares will be determined by factors such as relative supply of and demand for the Common Shares in the market, general market and economic circumstances, and other factors beyond the control of the Fund, the Fund cannot predict whether the Common Shares will trade at, below or above NAV. The Common Shares are designed primarily for long-term investors, and you should not view the Fund as a vehicle for trading purposes. Investment and Market Risk. An investment in the Common Shares is subject to investment risk, including the possible loss of the entire principal amount that you invest. Common Shares frequently trade at a discount to their NAV. Your investment in shares of the Fund represents an indirect investment in the securities owned by the Fund. Your shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of dividends and distributions, if applicable. Investors bear a risk of loss to the extent that the price at which they sell their shares is lower than at the time of purchase. The shares of the Fund are designed primarily for long-term investors, and you should not view the Fund as a vehicle for trading purposes. Leverage Risk. The use of leverage involves special risks for Common Shareholders, including the likelihood of greater volatility of net asset value and market price of, and distributions on, the Common Shares than a comparable portfolio without leverage. The use of leverage in a declining market will likely cause a greater decline in Common Share net asset value, which may result in a greater decline of the Common Share price, than if the Fund were not to have used leverage. 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, Preferred Share purchasers, liquidity providers, rating agencies that may rate the preferred securities, 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. From time to time, the Fund, Nuveen Fund Advisors and/or Nuveen Asset Management may be subject to pending or threatened litigation or regulatory action. Some of these claims may result in significant defense costs and potentially significant judgments. The ultimate outcome of any potential litigation or regulatory action or any claims that may arise in the future cannot be predicted and the reputation of the Fund, Nuveen Fund Advisors and/or Nuveen Asset Management could be damaged as a result. Certain litigation or regulatory scrutiny could materially adversely affect the Fund. The resolution of certain claims may result in significant fines, judgments, or settlements, which, if partially or completely uninsured, could adversely impact the Fund or the ability of Nuveen Fund Advisors and/or Nuveen Asset Management to perform their duties to the Fund. Global Economic Risk. The market value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably and for short or extended periods of time. Market values may change due to the particular circumstances of individual issuers or due to general conditions impacting issuers more broadly within a specific country, region, industry, sector or asset class. National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and securities prices around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies like China’s, may have global negative economic and market repercussions. As a result, the value of the Fund’s investments may be negatively affected whether or not the Fund invests in a country or region directly impacted by such conditions or events. 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. At any time after the date of this prospectus, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, securities held by the Fund or the issuers of such securities. Changing approaches to regulation may have a negative impact on the entities and/or securities in which the Fund invests. Legislation or regulation may also change the way in which the Fund itself is regulated. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objectives. 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. The Fund’s organizational documents include provisions that could limit the ability of other entities or persons to acquire control of the Fund or convert the Fund to open‑end status. Further, the By‑Laws provide that a shareholder who obtains beneficial ownership of Common Shares in a “Control Share Acquisition” shall have the same voting rights as other Common Shares only to the extent authorized by shareholders. Although the application of the “Control Share Acquisition” provisions has currently been suspended, these provisions could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares. See “Certain Provisions in the Declaration of Trust and By‑Laws.” Potential Conflicts of Interest Risk. Nuveen Fund Advisors and Nuveen Asset Management each provide a wide array of portfolio management and other asset management services to a mix of clients and may engage in ordinary course activities in which their respective interests or those of their clients may compete or conflict with those of the Fund. In certain circumstances, and subject to its fiduciary obligations under the Investment Advisers Act of 1940, Nuveen Asset Management may have to allocate a limited investment opportunity among its clients, which include closed‑end funds, open‑end funds and other commingled funds. Nuveen Fund Advisors and Nuveen Asset Management have each adopted policies and procedures designed to address such situations and other potential conflicts of interests. Economic and Political Events Risk. The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the municipal securities of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the creditworthiness and value of such municipal securities. Cybersecurity Risk. The Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. Cyber incidents may cause the Fund or its service providers to lose proprietary information, suffer data corruption, lose operational capacity or fail to comply with applicable privacy and other laws. Among other potentially harmful effects, cyber incidents also may result in theft, unauthorized monitoring and failures in the physical infrastructure or operating systems that support the Fund and its service providers. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. While the Fund’s service providers have established business continuity plans in the event of, and risk management systems to prevent, such cyber incidents, there are inherent limitations in such plans and systems including the possibility that certain risks have not been identified. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund. Unrated Securities Risk. The Fund may purchase securities that are not rated by any rating organization. Nuveen Asset Management may, after assessing such securities’ credit quality, internally assign ratings to certain of those securities in categories similar to those of rating organizations. Some unrated securities may not have an active trading market or may be difficult to value, which means the Fund might have difficulty selling them promptly at an acceptable price. To the extent that the Fund invests in unrated securities, the Fund’s ability to achieve its investment objectives will be more dependent on Nuveen Asset Management’s credit analysis than would be the case when the Fund invests in rated securities. Counterparty Risk. The Fund will be subject to credit risk with respect to the counterparties to the derivative transactions entered into by the Fund. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives transactions may affect the value of those instruments. Because certain derivative transactions in which the Fund may engage may be traded between counterparties based on contractual relationships, the Fund is subject to the risk that a counterparty will not perform its obligations under the related contracts. If a counterparty becomes bankrupt or otherwise becomes unable to perform its obligations due to financial difficulties the Fund may sustain losses (including the full amount of its investment), may be unable to liquidate a derivatives position or may experience significant delays in obtaining any recovery in bankruptcy or other reorganization proceedings. By entering into derivatives transactions, the Fund assumes the risk that its counterparties could experience such financial hardships. Although the Fund intends to enter into transactions only with counterparties that Nuveen Fund Advisors believes to be creditworthy, there can be no assurance that a counterparty will not default and that the Fund will not sustain a loss on a transaction. In the event of a counterparty’s bankruptcy or insolvency, any collateral posted by the Fund in connection with a derivatives transaction may be subject to the conflicting claims of that counterparty’s creditors, and the Fund may be exposed to the risk of a court treating the Fund as a general unsecured creditor of the counterparty, rather than as the owner of the collateral. 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 Fund’s Clearing Broker and Central Clearing Counterparty. The Commodity Exchange Act (the “CEA”) requires swaps and futures clearing brokers registered as “futures commission merchants” to segregate all funds received from customers with respect to any orders for the purchase or sale of U.S. domestic futures contracts and cleared swaps from the brokers’ proprietary assets. Similarly, the CEA requires each futures commission merchant to hold in separate secure accounts all funds received from customers with respect to any orders for the purchase or sale of foreign futures contracts and cleared swaps and segregate any such funds from the funds received with respect to domestic futures contracts. However, all funds and other property received by a clearing broker from its customers are held by the clearing broker on a commingled basis in an omnibus account and may be invested in certain instruments permitted under applicable regulations. There is a risk that assets deposited by the Fund with any swaps or futures clearing broker as margin for futures contracts or cleared swaps may, in certain circumstances, be used to satisfy losses of other clients of the Fund’s clearing broker. In addition, the assets of the Fund might not be fully protected in the event of the Fund’s clearing broker’s bankruptcy, as the Fund would be limited to recovering only a pro rata share of all available funds segregated on behalf of the clearing broker’s customers for the relevant account class. 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. The Fund’s annual portfolio turnover rate may vary greatly from year to year, as well as within a given year. The portfolio turnover rate is not considered a limiting factor in the execution of investment decisions for the Fund. High portfolio turnover may result in the realization of net short-term capital gains by the Fund which, when distributed to shareholders, will be taxable as ordinary income. In addition, a higher portfolio turnover rate would result in correspondingly greater brokerage and other transactional expenses that are borne by the Fund. Rating Agencies Risk. Rating agencies may fail to make timely changes in credit ratings and an issuer’s current financial condition may be better or worse than a rating indicates. In addition, rating agencies are subject to an inherent conflict of interest because they are often compensated by the same issuers whose securities they grade. |  |  |  |  |  |  |  |  |
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 as 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 |
May 2023 |  | $ | 13.86 |  |  | $ | 13.00 |  |  | $ | 14.10 |  |  | $ | 13.61 |  |  |  | 1.21 | % |  |  | (5.55 | )%
February 2023 |  | $ | 15.19 |  |  | $ | 13.10 |  |  | $ | 14.17 |  |  | $ | 13.70 |  |  |  | 7.89 | % |  |  | (5.42 | )%
November 2022 |  | $ | 13.98 |  |  | $ | 12.44 |  |  | $ | 13.83 |  |  | $ | 13.01 |  |  |  | 3.63 | % |  |  | (5.03 | )%
August 2022 |  | $ | 14.98 |  |  | $ | 12.95 |  |  | $ | 14.39 |  |  | $ | 13.71 |  |  |  | 5.05 | % |  |  | (6.09 | )%
May 2022 |  | $ | 16.00 |  |  | $ | 13.30 |  |  | $ | 15.19 |  |  | $ | 13.70 |  |  |  | 8.04 | % |  |  | (6.43 | )%
February 2022 |  | $ | 16.80 |  |  | $ | 14.71 |  |  | $ | 15.83 |  |  | $ | 15.07 |  |  |  | 8.93 | % |  |  | (4.11 | )%
November 2021 |  | $ | 16.53 |  |  | $ | 15.26 |  |  | $ | 15.96 |  |  | $ | 15.70 |  |  |  | 3.64 | % |  |  | (3.48 | )%
August 2021 |  | $ | 17.30 |  |  | $ | 16.13 |  |  | $ | 16.14 |  |  | $ | 15.96 |  |  |  | 7.99 | % |  |  | 0.25 | %
May 2021* |  | $ | 19.40 |  |  | $ | 15.92 |  |  | $ | 16.01 |  |  | $ | 15.85 |  |  |  | 21.25 | % |  |  | (0.31 | )%
* | For the fiscal quarter April 1, 2021 through May 31, 2021.
The net asset value per Common Share, the market price and percentage of discount to net asset value per Common Share on July 18, 2023 were $13.85, $13.35 and (3.61)%, respectively. As of July 18, 2023, the Fund had 6,362,276 Common Shares outstanding and net assets of $88,146,607. |  |  |  |  |  |  |  |  |
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 July 18, 2023:
Title of Class |  | Amount Authorized |  |  | Amount Held by the Fund or for its Account |  |  | Amount Outstanding |
Common |  |  | unlimited |  |  |  | — |  |  | $ | 6,362,276 |
Municipal Securities Market Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Municipal Securities Market Risk. The amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the investment performance of the Fund may therefore be more dependent on the analytical abilities of Nuveen Asset Management than if the Fund were a stock fund or taxable bond fund. The secondary market for municipal securities, particularly the below investment grade bonds in which the Fund may invest, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices. In addition, the market for below investment grade municipal securities has experienced in the past, and may experience in the future, periods of significant volatility, which could negatively impact the value of the municipal securities in the Fund’s portfolio and the market price of the Common Shares. 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. Issuers of securities in which the Fund may invest may default on their obligations to pay principal or interest when due. This non‑payment would result in a reduction of income to the Fund, a reduction in the value of a debt security experiencing non‑payment and, potentially, a decrease in the NAV of the Fund. With respect to the Fund’s investments in securities that are secured, there can be no assurance that liquidation of collateral would satisfy the issuer’s obligation in the event of non‑payment of a scheduled interest or principal payment or that such collateral could be readily liquidated. In the event of the bankruptcy of an issuer the Fund could experience delays or limitations with respect to its ability to realize the benefits of any collateral securing a security. To the extent that the credit rating assigned to a security in the Fund’s portfolio is downgraded, the market price and liquidity of such security may be adversely affected. |  |  |  |  |  |  |  |  |
Credit Spread Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Credit Spread Risk. Credit spread risk is the risk that credit spreads (i.e., the difference in yield between securities that is due to differences in their credit quality) may increase when the market believes that municipal securities generally have a greater risk of default. Increasing credit spreads may reduce the market values of the Fund’s securities. Credit spreads often increase more for lower rated and unrated securities than for investment grade securities. In addition, when credit spreads increase, reductions in market value will generally be greater for longer-maturity securities. |  |  |  |  |  |  |  |  |
Below Investment Grade Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Below Investment Grade Risk. Debt instruments of below investment grade quality are regarded as having predominately speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal, and are commonly referred to as junk bonds or high yield debt, which implies higher price volatility and default risk than investment grade instruments of comparable terms and duration. Issuers of lower grade instruments may be highly leveraged and may not have available to them more traditional methods of financing. The prices of these lower grade instruments are typically more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn, than are the prices of higher grade instruments. 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. Interest rate risk is the risk that debt securities in the Fund’s portfolio will decline in value because of changes in market interest rates. Generally, when market interest rates rise, the market value of such securities will fall, and vice versa. As interest rates decline, issuers of debt securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower-yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower than expected principal payments may extend the average life of securities, potentially locking in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer-term debt securities generally fluctuate more than prices of shorter-term debt securities as interest rates change. As of the date of this Prospectus, the risk of rising interest rates may be greater than would normally be the case due to the current changes in government fiscal policy initiatives and resulting market reaction to those initiatives. Because the market price of debt securities may change based upon investors’ collective perceptions of future earnings, the value of the Fund will generally decline when investors anticipate or experience rising interest rates. |  |  |  |  |  |  |  |  |
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. To the extent that a debt security continues to use LIBOR as a benchmark or reference rate for interest rate calculations, such security is subject to risks related to the transition from LIBOR to the Secured Overnight Funding Rate (“SOFR”). SOFR has been selected by a committee established by the Board of Governors of the Federal Reserve System and the Federal Reserve Bank of New York to replace LIBOR as a reference rate for certain financial contracts in the United States after June 30, 2023. However, there remains uncertainty regarding the new replacement rate as well as the impact of the transition from LIBOR on the Fund and the financial markets generally. Other countries have undertaken similar initiatives to identify replacement reference rates in their respective markets. The transition process, or the failure of an industry to transition, could lead to increased volatility and illiquidity in markets for instruments that currently rely on LIBOR to determine interest rates, and a reduction in the values of some LIBOR-based investments, all of which could impact the Fund. |  |  |  |  |  |  |  |  |
Duration Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Duration Risk. Duration is the sensitivity, expressed in years, of the price of a fixed-income security to changes in the general level of interest rates (or yields). Securities with longer durations tend to be more sensitive to interest rate (or yield) changes, which typically corresponds to increased volatility and risk, than securities with shorter durations. For example, if a security or portfolio has a duration of three years and interest rates increase by 1%, then the security or portfolio would decline in value by approximately 3%. Duration differs from maturity in that it considers potential changes to interest rates, and a security’s coupon payments, yield, price and par value and call features, in addition to the amount of time until the security matures. The duration of a security will be expected to change over time with changes in market factors and time to maturity. |  |  |  |  |  |  |  |  |
Call Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Call Risk. The Fund may invest in debt securities that are subject to call risk. Such municipal securities may be redeemed at the option of the issuer, or “called,” before their stated maturity or redemption date. In general, an issuer will call its instruments if they can be refinanced by issuing new instruments which bear a lower interest rate. The Fund is subject to the possibility that during periods of falling interest rates, an issuer will call its high yielding municipal securities. The Fund would then be forced to invest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund’s income. |  |  |  |  |  |  |  |  |
Prepayment Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Prepayment Risk. Prepayment risk is the risk that the issuer of a debt security will repay principal (in part or in whole) prior to the scheduled maturity date. Debt securities allowing prepayment may offer less potential for gains during a period of declining interest rates, as the Fund may be required to reinvest the proceeds of any prepayment at lower interest rates, reducing its income. If the Fund purchased the debt securities at a premium, prepayments on the securities could cause the Fund to lose a portion of its principal investment. These factors may cause the value of an investment in the Fund to change. The impact of prepayments on the price of a debt security may be difficult to predict and may increase the security’s volatility. |  |  |  |  |  |  |  |  |
Reinvestment Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called securities at market interest rates that are below the portfolio’s current earnings rate. A decline in income could affect the Common Shares’ market price, NAV and/or a Common Shareholder’s overall returns. |  |  |  |  |  |  |  |  |
Alternative Minimum Tax Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Alternative Minimum Tax Risk. The Fund may invest in AMT Bonds. Therefore, a portion of the Fund’s otherwise exempt-interest dividends may be taxable to those shareholders subject to the federal alternative minimum tax. |  |  |  |  |  |  |  |  |
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. Typically, inverse floating rate securities represent beneficial interests in a special purpose trust (sometimes called a “tender option bond trust”) formed for the purpose of holding municipal bonds. See “The Fund’s Investments—Portfolio Composition—Municipal Securities—Inverse Floating Rate Securities.” In general, income on inverse floating rate securities will decrease when short-term interest rates increase and increase when short-term interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal. 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. Inventories of municipal securities held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell municipal securities at attractive prices, and increase municipal security price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. The secondary market for municipal securities, particularly the below investment grade municipal securities in which the Fund may invest, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of municipal securities to raise cash to meet its obligations, those sales could further reduce the municipal securities’ prices and hurt performance. The Fund may invest a significant portion of its assets in unrated municipal securities. The market for these municipal securities may be less liquid than the market for rated municipal securities of comparable quality. Less public information is typically available about unrated municipal securities or issuers than rated municipal securities or issuers. |  |  |  |  |  |  |  |  |
Special Risks Related to Certain Municipal Obligations [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Special Risks Related to Certain Municipal Obligations. Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non‑appropriation” clauses that relieve the governmental issuer of any obligation to make future payments under the lease or contract unless money is appropriated for such purpose by the appropriate legislative body. In addition, such leases or contracts may be subject to the temporary abatement of payments in the event that the governmental issuer is prevented from maintaining occupancy of the leased premises or utilizing the leased equipment. Although the obligations may be secured by the leased equipment or facilities, the disposition of the property in the event of non‑appropriation or foreclosure might prove difficult, time consuming and costly, and may result in a delay in recovering or the failure to fully recover the Fund’s original investment. In the event of non‑appropriation, the issuer would be in default and taking ownership of the assets may be a remedy available to the Fund, although the Fund does not anticipate that such a remedy would normally be pursued. To the extent that the Fund invests in unrated municipal leases or participates in such leases, the credit quality rating and risk of cancellation of such unrated leases will be monitored on an ongoing basis. 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. Illiquid investments are securities that are not readily marketable. These securities may include restricted securities, which cannot be resold to the public without an effective registration statement under the 1933 Act, or, if they are unregistered, may be 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. The Fund may invest in low‑rated securities or securities unrated but judged by the sub‑adviser to be of comparable quality. Some or many of these low‑rated securities, although not in default, may be “distressed,” meaning that the issuer is experiencing financial difficulties or distress at the time of acquisition. Such securities would present a substantial risk of future default which may cause the Fund to incur losses, including additional expenses, to the extent it is required to seek recovery upon a default in the payment of principal or interest on those securities. In any reorganization or liquidation proceeding relating to a portfolio security, the Fund may lose its entire investment or may be required to accept cash or securities with a value less than its original investment. Distressed securities may be subject to restrictions on resale. |  |  |  |  |  |  |  |  |
Derivatives Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Derivatives Risk. The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a municipal security or other asset without buying or selling the municipal security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over‑the‑counter derivative transaction between the Fund and a counterparty that is not cleared through a central counterparty also involves the risk that a loss may be sustained as a result of the failure of the counterparty to the contract to make required payments. The payment obligation for a cleared derivative transaction is guaranteed by a central counterparty, which exposes the Fund to the creditworthiness of the central counterparty. It is possible that developments in the derivatives market, including changes in government regulation, could adversely impact the Fund’s ability to invest in certain derivatives. 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 may enter into debt-related derivatives instruments such as credit default swap contracts and interest rate swaps. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by Nuveen Asset Management not only of the referenced asset, rate or index, but also of the swap itself. If Nuveen Fund Advisors and/or Nuveen Asset Management is incorrect in its forecasts of default risks, market spreads or other applicable factors or events, the investment performance of the Fund would diminish compared with what it would have been if these techniques were not used. As the protection seller in a credit default swap, the Fund effectively adds leverage to its portfolio because, in addition to being subject to investment exposure on its total net assets, the Fund is subject to investment exposure on the notional amount of the swap. 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. The Fund may use certain transactions for hedging the portfolio’s exposure to credit risk and the risk of increases in interest rates, which could result in poorer overall performance for the Fund. The Fund’s use of certain transactions to reduce risk involves costs and will be subject to Nuveen Asset Management’s ability to predict correctly changes in the relationships of such hedge 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. 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 Commodity Futures Trading Commission (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. The Fund’s use of derivatives or other transactions to reduce risks involves costs and will be subject to Nuveen Asset Management’s ability to predict correctly changes in the relationships of such hedge 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. |  |  |  |  |  |  |  |  |
Concentration Risk in California Issuers [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Concentration Risk in California Issuers. The Fund’s policy of investing in municipal securities of issuers located in California makes the Fund more susceptible to the adverse economic, political or regulatory occurrences affecting such issuers. The information set forth below and the related information in Appendix A of this Prospectus is derived from sources that are generally available to investors. The information is intended to give a recent historical description and is not intended to indicate future or continuing trends in the financial or other positions of California. It should be noted that the creditworthiness of obligations issued by local California issuers may be unrelated to the creditworthiness of obligations issued by the State of California, and that there is no obligation on the part of the State to make payment on such local obligations in the event of default. California is subject to large fluctuations in its tax revenue and fixed spending obligations. During recessionary periods, which California recently experienced, dramatic cuts to programs and/or tax increases may be required. To address budget gaps from the recent recessionary period, spending was cut, State programs were realigned to local governments, and short-term budgetary solutions were implemented. Despite the recent significant budgetary improvements and moderate growth, a number of major risks and pressures threaten the State’s financial condition, including the need to repay billions of dollars of obligations that were deferred to balance budgets during the economic downturn. Continued risks to the State’s long-term stability include pension liabilities, debt and increasing annual obligations, and potential cost increases associated with the federal deficit. California’s fiscal situation heightens the risk of investing in bonds issued by the State and its political subdivisions, agencies, instrumentalities and authorities, including the risk of default, and also heightens the risk that the prices of California municipal securities, and the Fund’s net asset value, will experience greater volatility. As of June 30, 2023, California general obligation bonds were rated “Aa2” by Moody’s, “AA‑” with Positive Outlook by S&P and “AA” by Fitch. There can be no assurance that such ratings will be maintained in the future. The State’s credit rating, and any future revisions or withdrawal of a credit rating, could have a negative effect on the market price of the State’s general obligation bonds, as well as notes and bonds issued by California’s public authorities and local governments. Lower credit ratings make it more expensive for the State to raise revenue, and in some cases, could prevent the State from issuing general obligation bonds in the quantity otherwise desired. Further, downgrades can negatively impact the marketability and price of securities in the Fund’s portfolio. The foregoing information constitutes only a brief summary of some of the general factors that may impact certain issuers of municipal bonds and does not purport to be a complete or exhaustive description of all adverse conditions to which the issuers of municipal bonds held by the Fund are subject. Additionally, many factors, including national economic, social and environmental policies and conditions, which are not within the control of the issuers of the municipal bonds, could affect or could have an adverse impact on the financial condition of the issuers. The Fund is unable to predict whether or to what extent such factors or other factors may affect the issuers of the municipal securities, the market value or marketability of the municipal securities or the ability of the respective issuers of the municipal bonds acquired by the Fund to pay interest on or principal of the municipal securities. This information has not been independently verified. See Appendix A of this Prospectus for a further discussion of factors affecting municipal securities in California. |  |  |  |  |  |  |  |  |
Puerto Rico Municipal Securities Market Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Puerto Rico Municipal Securities Market Risk. To the extent that the Fund invests a significant portion of its assets in the securities issued by the Commonwealth of Puerto Rico or its political subdivisions, agencies, instrumentalities, or public corporations (collectively referred to in this Prospectus as “Puerto Rico” or the “Commonwealth”), it will be disproportionally affected by political, social and economic conditions and developments in the Commonwealth. In addition, economic, political or regulatory changes in that territory could adversely affect the value of the Fund’s investment portfolio. 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. At times, the Fund may focus its investments (i.e., overweight its investments relative to the overall municipal securities market) in one or more particular sectors, which may subject the Fund to additional risk and variability. Securities issued in the same sector may be similarly affected by economic or market events, making the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. As the percentage of the Fund’s Managed Assets invested in a particular sector increases, so does the potential for fluctuation in the NAV of the Common Shares. |  |  |  |  |  |  |  |  |
Sector and Industry Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Sector and Industry Risk. Subject to the concentration limits of the Fund’s investment policies and guidelines, the Fund may invest a significant portion of its net assets in certain sectors of the municipal securities market, such as hospitals and other health care facilities, charter schools and other private educational facilities, special taxing districts and start‑up utility districts, and private activity bonds including industrial development bonds on behalf of transportation companies such as airline companies, whose credit quality and performance may be more susceptible to economic, business, political, regulatory and other developments than other sectors of municipal issuers. If the Fund invests a significant portion of its net assets in the sectors noted above, the Fund’s performance may be subject to additional risk and variability. |  |  |  |  |  |  |  |  |
Economic Sector Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Economic Sector Risk. The Fund may invest a significant amount of its total assets in municipal securities in the same economic sector. This may make the Fund more susceptible to adverse economic, political or regulatory occurrences affecting an economic sector. As concentration increases, so does the potential for fluctuation in the value of the Fund’s assets. In addition, the Fund may invest a significant portion of its assets in certain sectors of the municipal securities market, such as hospitals and other health care facilities, charter schools and other private educational facilities, special taxing districts and start‑up utility districts, and private activity bonds including industrial development bonds on behalf of transportation companies such as airline companies, whose credit quality and performance may be more susceptible to economic, business, political, regulatory and other developments than other sectors of municipal issuers. If the Fund invests a significant portion of its assets in the sectors noted above, the Fund’s performance may be subject to additional risk and variability. 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. The Fund’s income is based primarily on the interest it earns from its investments, which can vary widely over the short and long term. The Fund’s income could decline due to falling market interest rates. This is because, in a falling interest rate environment, the Fund generally will have to invest the proceeds from maturing portfolio securities in lower-yielding securities. This risk is magnified when prevailing short-term interest rates increase and the Fund holds residual interest municipal bonds. |  |  |  |  |  |  |  |  |
Inflation Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Inflation Risk. Inflation is the reduction in the purchasing power of money resulting from the increase in the price of goods and services. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the Common Shares and distributions can decline. |  |  |  |  |  |  |  |  |
Deflation Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Deflation Risk. Deflation risk is the risk that prices throughout the economy decline over time, which may have an adverse effect on the market valuation of companies, their assets and revenues. In addition, deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. |  |  |  |  |  |  |  |  |
Zero Coupon Bonds Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Zero Coupon Bonds Risk. Because interest on zero coupon bonds is not paid on a current basis, the values of zero coupon bonds will be more volatile in response to interest rate changes than the values of bonds that distribute income regularly. Although zero coupon bonds generate income for accounting purposes, they do not produce cash flow, and thus the Fund could be forced to liquidate securities at an inopportune time in order to generate cash to distribute to shareholders as required by tax laws. |  |  |  |  |  |  |  |  |
Tax Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Tax Risk. To qualify for the favorable U.S. federal income tax treatment generally accorded to a RIC under Subchapter M of the Code the Fund must, among other requirements, derive in each taxable year at least 90% of its gross income from certain prescribed sources and satisfy a diversification test on a quarterly basis. If the Fund fails to satisfy the qualifying income or diversification requirements in any taxable year, the Fund may be eligible for relief provisions if the failures are due to reasonable cause and not willful neglect and if a penalty tax is paid with respect to each failure to satisfy the applicable requirements. Additionally, relief is provided for certain de minimis failures of the diversification requirements where the Fund corrects the failure within a specified period. In order to be eligible for the relief provisions with respect to a failure to meet the diversification requirements, the Fund may be required to dispose of certain assets. If these relief provisions were not available to the Fund and it were to fail to qualify for treatment as a RIC for a taxable year, all of its taxable income (including its net capital gain) would be subject to tax at the 21% regular corporate rate without any deduction for distributions to shareholders, and such distributions would be taxable as ordinary dividends to the extent of the Fund’s current and accumulated earnings and profits. 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 is not 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. The Fund will invest in municipal securities in reliance at the time of purchase on an opinion of bond counsel to the issuer that the interest paid on those securities will be excludable from gross income for regular federal income tax purposes, and neither Nuveen Asset Management nor any other person will independently verify that opinion. Subsequent to the Fund’s acquisition of such a municipal security, however, the security may be determined to pay, or to have paid, taxable income. Distributions of taxable ordinary taxable 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. See “Tax Matters.” |  |  |  |  |  |  |  |  |
Insurance Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Insurance Risk. The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub‑prime mortgages and other lower credit quality investments that have experienced defaults or otherwise suffered extreme credit deterioration. As a result, such losses have reduced the insurers’ capital and called into question their continued ability to perform their obligations under such insurance if they are called upon to do so in the future. While an insured municipal security will typically be deemed to have the rating of its insurer, if the insurer of a municipal security suffers a downgrade in its credit rating or the market discounts the value of the insurance provided by the insurer, the rating of the underlying municipal security will be more relevant and the value of the municipal security would more closely, if not entirely, reflect such rating. In such a case, the value of insurance associated with a municipal security would decline and may not add any value. The insurance feature of a municipal security does not guarantee the full payment of principal and interest through the life of an insured obligation, the market value of the insured obligation or the NAV represented by such insured obligation. |  |  |  |  |  |  |  |  |
Tobacco Settlement Bond Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Tobacco Settlement Bond Risk. Tobacco settlement bonds are municipal securities that are backed solely by expected revenues to be derived from lawsuits involving tobacco related deaths and illnesses which were settled between certain states and American tobacco companies. Tobacco settlement bonds are secured by an issuing state’s proportionate share in the Master Settlement Agreement (“MSA”). The MSA is an agreement reached out of court in November 1998 between 46 states and nearly all of the U.S. tobacco manufacturers. Under the terms of the MSA, the actual amount of future settlement payments by tobacco manufacturers is dependent on many factors, including, but not limited to, annual domestic cigarette shipments, reduced cigarette consumption, increased taxes on cigarettes, inflation, financial capability of tobacco companies, continuing litigation and the possibility of tobacco manufacturer bankruptcy. Payments made by tobacco manufacturers could be negatively impacted if the decrease in tobacco consumption is significantly greater than the forecasted decline. |  |  |  |  |  |  |  |  |
Valuation Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Valuation Risk. The municipal securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including readily available market quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to sell a portfolio security at the price established by the pricing service, which could result in a loss to the Fund. Pricing services generally price municipal securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Different pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s NAV. |  |  |  |  |  |  |  |  |
Other Investment Companies Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Other Investment Companies Risk. The Fund may invest in the securities of other investment companies, including ETFs. Investing in an investment company exposes the Fund to all of the risks of that investment company’s investments. The Fund, as a holder of the securities of other investment companies, will bear its pro rata portion of the other investment companies’ expenses, including advisory fees. These expenses are in addition to the direct expenses of the Fund’s own operations. As a result, the cost of investing in investment company 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. Shares of closed‑end investment companies like the Fund frequently trade at prices lower than their NAV. This characteristic is a risk separate and distinct from the risk that the Fund’s NAV could decrease as a result of investment activities. Whether investors will realize gains or losses upon the sale of the Common Shares will depend not upon the Fund’s NAV but entirely upon whether the market price of the Common Shares at the time of sale is above or below the investor’s purchase price for the Common Shares. Furthermore, management may have difficulty meeting the Fund’s investment objectives and managing its portfolio when the underlying securities are redeemed or sold during periods of market turmoil and as investors’ perceptions regarding closed‑end funds or their underlying investments change. Because the market price of the Common Shares will be determined by factors such as relative supply of and demand for the Common Shares in the market, general market and economic circumstances, and other factors beyond the control of the Fund, the Fund cannot predict whether the Common Shares will trade at, below or above NAV. The Common Shares are designed primarily for long-term investors, and you should not view the Fund as a vehicle for trading purposes. |  |  |  |  |  |  |  |  |
Investment and Market Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Investment and Market Risk. An investment in the Common Shares is subject to investment risk, including the possible loss of the entire principal amount that you invest. Common Shares frequently trade at a discount to their NAV. Your investment in shares of the Fund represents an indirect investment in the securities owned by the Fund. Your shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of dividends and distributions, if applicable. Investors bear a risk of loss to the extent that the price at which they sell their shares is lower than at the time of purchase. The shares of the Fund are designed primarily for long-term investors, and you should not view the Fund as a vehicle for trading purposes. |  |  |  |  |  |  |  |  |
Leverage Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Leverage Risk. The use of leverage involves special risks for Common Shareholders, including the likelihood of greater volatility of net asset value and market price of, and distributions on, the Common Shares than a comparable portfolio without leverage. The use of leverage in a declining market will likely cause a greater decline in Common Share net asset value, which may result in a greater decline of the Common Share price, than if the Fund were not to have used leverage. 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, Preferred Share purchasers, liquidity providers, rating agencies that may rate the preferred securities, 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. From time to time, the Fund, Nuveen Fund Advisors and/or Nuveen Asset Management may be subject to pending or threatened litigation or regulatory action. Some of these claims may result in significant defense costs and potentially significant judgments. The ultimate outcome of any potential litigation or regulatory action or any claims that may arise in the future cannot be predicted and the reputation of the Fund, Nuveen Fund Advisors and/or Nuveen Asset Management could be damaged as a result. Certain litigation or regulatory scrutiny could materially adversely affect the Fund. The resolution of certain claims may result in significant fines, judgments, or settlements, which, if partially or completely uninsured, could adversely impact the Fund or the ability of Nuveen Fund Advisors and/or Nuveen Asset Management to perform their duties to the Fund. |  |  |  |  |  |  |  |  |
Global Economic Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Global Economic Risk. The market value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably and for short or extended periods of time. Market values may change due to the particular circumstances of individual issuers or due to general conditions impacting issuers more broadly within a specific country, region, industry, sector or asset class. National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and securities prices around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies like China’s, may have global negative economic and market repercussions. As a result, the value of the Fund’s investments may be negatively affected whether or not the Fund invests in a country or region directly impacted by such conditions or events. 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. At any time after the date of this prospectus, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, securities held by the Fund or the issuers of such securities. Changing approaches to regulation may have a negative impact on the entities and/or securities in which the Fund invests. Legislation or regulation may also change the way in which the Fund itself is regulated. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objectives. 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. The Fund’s organizational documents include provisions that could limit the ability of other entities or persons to acquire control of the Fund or convert the Fund to open‑end status. Further, the By‑Laws provide that a shareholder who obtains beneficial ownership of Common Shares in a “Control Share Acquisition” shall have the same voting rights as other Common Shares only to the extent authorized by shareholders. Although the application of the “Control Share Acquisition” provisions has currently been suspended, these provisions could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares. See “Certain Provisions in the Declaration of Trust and By‑Laws.” |  |  |  |  |  |  |  |  |
Potential Conflicts of Interest Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Potential Conflicts of Interest Risk. Nuveen Fund Advisors and Nuveen Asset Management each provide a wide array of portfolio management and other asset management services to a mix of clients and may engage in ordinary course activities in which their respective interests or those of their clients may compete or conflict with those of the Fund. In certain circumstances, and subject to its fiduciary obligations under the Investment Advisers Act of 1940, Nuveen Asset Management may have to allocate a limited investment opportunity among its clients, which include closed‑end funds, open‑end funds and other commingled funds. Nuveen Fund Advisors and Nuveen Asset Management have each adopted policies and procedures designed to address such situations and other potential conflicts of interests. |  |  |  |  |  |  |  |  |
Economic and Political Events Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Economic and Political Events Risk. The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the municipal securities of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the creditworthiness and value of such municipal securities. |  |  |  |  |  |  |  |  |
Cybersecurity Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Cybersecurity Risk. The Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. Cyber incidents may cause the Fund or its service providers to lose proprietary information, suffer data corruption, lose operational capacity or fail to comply with applicable privacy and other laws. Among other potentially harmful effects, cyber incidents also may result in theft, unauthorized monitoring and failures in the physical infrastructure or operating systems that support the Fund and its service providers. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. While the Fund’s service providers have established business continuity plans in the event of, and risk management systems to prevent, such cyber incidents, there are inherent limitations in such plans and systems including the possibility that certain risks have not been identified. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund. |  |  |  |  |  |  |  |  |
Unrated Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Unrated Securities Risk. The Fund may purchase securities that are not rated by any rating organization. Nuveen Asset Management may, after assessing such securities’ credit quality, internally assign ratings to certain of those securities in categories similar to those of rating organizations. Some unrated securities may not have an active trading market or may be difficult to value, which means the Fund might have difficulty selling them promptly at an acceptable price. To the extent that the Fund invests in unrated securities, the Fund’s ability to achieve its investment objectives will be more dependent on Nuveen Asset Management’s credit analysis than would be the case when the Fund invests in rated securities. |  |  |  |  |  |  |  |  |
Counterparty Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Counterparty Risk. The Fund will be subject to credit risk with respect to the counterparties to the derivative transactions entered into by the Fund. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives transactions may affect the value of those instruments. Because certain derivative transactions in which the Fund may engage may be traded between counterparties based on contractual relationships, the Fund is subject to the risk that a counterparty will not perform its obligations under the related contracts. If a counterparty becomes bankrupt or otherwise becomes unable to perform its obligations due to financial difficulties the Fund may sustain losses (including the full amount of its investment), may be unable to liquidate a derivatives position or may experience significant delays in obtaining any recovery in bankruptcy or other reorganization proceedings. By entering into derivatives transactions, the Fund assumes the risk that its counterparties could experience such financial hardships. Although the Fund intends to enter into transactions only with counterparties that Nuveen Fund Advisors believes to be creditworthy, there can be no assurance that a counterparty will not default and that the Fund will not sustain a loss on a transaction. In the event of a counterparty’s bankruptcy or insolvency, any collateral posted by the Fund in connection with a derivatives transaction may be subject to the conflicting claims of that counterparty’s creditors, and the Fund may be exposed to the risk of a court treating the Fund as a general unsecured creditor of the counterparty, rather than as the owner of the collateral. 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. The Commodity Exchange Act (the “CEA”) requires swaps and futures clearing brokers registered as “futures commission merchants” to segregate all funds received from customers with respect to any orders for the purchase or sale of U.S. domestic futures contracts and cleared swaps from the brokers’ proprietary assets. Similarly, the CEA requires each futures commission merchant to hold in separate secure accounts all funds received from customers with respect to any orders for the purchase or sale of foreign futures contracts and cleared swaps and segregate any such funds from the funds received with respect to domestic futures contracts. However, all funds and other property received by a clearing broker from its customers are held by the clearing broker on a commingled basis in an omnibus account and may be invested in certain instruments permitted under applicable regulations. There is a risk that assets deposited by the Fund with any swaps or futures clearing broker as margin for futures contracts or cleared swaps may, in certain circumstances, be used to satisfy losses of other clients of the Fund’s clearing broker. In addition, the assets of the Fund might not be fully protected in the event of the Fund’s clearing broker’s bankruptcy, as the Fund would be limited to recovering only a pro rata share of all available funds segregated on behalf of the clearing broker’s customers for the relevant account class. 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. The Fund’s annual portfolio turnover rate may vary greatly from year to year, as well as within a given year. The portfolio turnover rate is not considered a limiting factor in the execution of investment decisions for the Fund. High portfolio turnover may result in the realization of net short-term capital gains by the Fund which, when distributed to shareholders, will be taxable as ordinary income. In addition, a higher portfolio turnover rate would result in correspondingly greater brokerage and other transactional expenses that are borne by the Fund. |  |  |  |  |  |  |  |  |
Rating Agencies Risk [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  | Rating Agencies Risk. Rating agencies may fail to make timely changes in credit ratings and an issuer’s current financial condition may be better or worse than a rating indicates. In addition, rating agencies are subject to an inherent conflict of interest because they are often compensated by the same issuers whose securities they grade. |  |  |  |  |  |  |  |  |
Business Contact [Member] |  |  |  |  |  |  |  |  |  |  |
Cover [Abstract] |  |  |  |  |  |  |  |  |  |  |
Entity Address, Address Line One |  | 333 West Wacker Drive |  |  |  |  |  |  |  |  |
Entity Address, City or Town |  | Chicago |  |  |  |  |  |  |  |  |
Entity Address, State or Province |  | IL |  |  |  |  |  |  |  |  |
Entity Address, Postal Zip Code |  | 60606 |  |  |  |  |  |  |  |  |
Contact Personnel Name |  | Mark L. Winget |  |  |  |  |  |  |  |  |
Common Shares [Member] |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |
Lowest Price or Bid |  |  | $ 13.00 | $ 13.10 | $ 12.44 | $ 12.95 | $ 13.30 | $ 14.71 | $ 15.26 | $ 16.13 | $ 15.92
Highest Price or Bid |  |  | 13.86 | 15.19 | 13.98 | 14.98 | 16.00 | 16.80 | 16.53 | 17.30 | 19.40
Lowest Price or Bid, NAV |  |  | 13.61 | 13.70 | 13.01 | 13.71 | 13.70 | 15.07 | 15.70 | 15.96 | 15.85
Highest Price or Bid, NAV |  |  | $ 14.10 | $ 14.17 | $ 13.83 | $ 14.39 | $ 15.19 | $ 15.83 | $ 15.96 | $ 16.14 | $ 16.01
Highest Price or Bid, Premium (Discount) to NAV [Percent] |  |  | 1.21% | 7.89% | 3.63% | 5.05% | 8.04% | 8.93% | 3.64% | 7.99% | 21.25%
Lowest Price or Bid, Premium (Discount) to NAV [Percent] |  |  | (5.55%) | (5.42%) | (5.03%) | (6.09%) | (6.43%) | (4.11%) | (3.48%) | 0.25% | (0.31%)
Latest Share Price |  | $ 13.35 |  |  |  |  |  |  |  |  |
Latest Premium (Discount) to NAV [Percent] |  | (3.61%) |  |  |  |  |  |  |  |  |
Latest NAV |  | $ 13.85 |  |  |  |  |  |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |  |  |  |  |  |  |  |
Outstanding Security, Title [Text Block] |  | Common |  |  |  |  |  |  |  |  |
Outstanding Security, Held [Shares] |  |  |  |  |  |  |  |  |  |  |
Outstanding Security, Not Held [Shares] |  | 6,362,276 |  |  |  |  |  |  |  |  |
[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 February 28, 2023.
[3] | Assuming a Common Share offering price of $13.35 (the Fund’s closing price on the NYSE on July 18, 2023).
[4] | 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 “Portfolio Composition—Other Investment Companies” in the SAI.
[5] | For the fiscal quarter April 1, 2021 through May 31, 2021.

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