Common shareholder transaction expenses
Sales load paid by you (as a percentage of offering price)	— ¹
Offering expenses (as a percentage of offering price)	None ²
Dividend reinvestment plan fees	$5.00³

¹If common shares are sold to or through underwriters, the Prospectus Supplement will set forth any applicable sales load.

²Eaton Vance Management (“EVM”) will pay the expenses of the offering (other than the applicable commissions); therefore, offering expenses are not included in the Summary of Fund Expenses. Offering expenses generally include, but are not limited to, the preparation, review and filing with the SEC of the Trust’s registration statement (including its current Prospectus Supplement, the accompanying Prospectus and Statement of Additional Information (“SAI”)), the preparation, review and filing of any associated marketing or similar materials, costs associated with the printing, mailing or other distribution of its current Prospectus Supplement, the accompanying Prospectus, SAI and/or marketing materials, associated filing fees, stock exchange listing fees, and legal and auditing fees associated with the offering.

³You will be charged a $5.00 service charge and pay brokerage charges if you direct the plan agent to sell your common shares held in a dividend reinvestment account.

Sales Load [Percent]

^[1]

Dividend Reinvestment and Cash Purchase Fees

^[2]

$ 5.00

Other Transaction Expenses [Abstract]

Other Transaction Expenses [Percent]

^[3]

0.00%

Annual Expenses [Table Text Block]

Annual expenses	Percentage of net assets attributable to common shares⁴
Investment adviser fee	0.67%⁵
Interest expense	0.32⁶
Other expenses	0.10
Total annual Fund operating expenses	1.09%

⁴Stated as a percentage of average net assets attributable to common shares for the year ended March 31, 2023.

⁵The investment adviser fee paid by the Trust to EVM is based on the average daily gross assets of the Trust, including all assets attributable to any form of investment leverage that the Trust may utilize. Accordingly, if the Trust were to increase investment leverage in the future, the investment adviser fee will increase as a percentage of net assets.

⁶Interest expense relates to the Trust’s liability with respect to floating-rate notes held by third parties in conjunction with investments in residual interest bonds. The Trust records offsetting interest income in an amount at least equal to this expense relating to the municipal obligations underlying such transactions.

Management Fees [Percent]

^[4],[5]

0.67%

Interest Expenses on Borrowings [Percent]

^[4],[6]

0.32%

Other Annual Expenses [Abstract]

Other Annual Expenses [Percent]

^[4]

0.10%

Total Annual Expenses [Percent]

^[4]

1.09%

Expense Example [Table Text Block]

Example

The following Example illustrates the expenses that common shareholders would pay on a $1,000 investment in common shares, assuming (i) total annual expenses of 1.09% of net assets attributable to common shares in years 1 through 10; (ii) a 5% annual return; and (iii) all distributions are reinvested at NAV:

1 Year	3 Years	5 Years	10 Years
$11	$35	$60	$133

The above table and example and the assumption in the example of a 5% annual return are required by regulations of the U.S. Securities and Exchange Commission (“SEC”) that are applicable to all investment companies; the assumed 5% annual return is not a prediction of, and does not represent, the projected or actual performance of the Trust’s common shares. In addition, while the example assumes reinvestment of all dividends and distributions at NAV, participants in the Trust’s dividend reinvestment plan may receive common shares purchased or issued at a price or value different from NAV. The example does not include sales load or estimated offering costs, which would cause the expenses shown in the example to increase.

The example should not be considered a representation of past or future expenses, and the Trust’s actual expenses may be greater or less than those shown. Moreover, the Trust’s actual rate of return may be greater or less than the hypothetical 5% return shown in the example.

Expense Example, Year 01

$ 11

Expense Example, Years 1 to 3

Expense Example, Years 1 to 5

Expense Example, Years 1 to 10

$ 133

Purpose of Fee Table , Note [Text Block]

The purpose of the table below is to help you understand all fees and expenses that you, as a common shareholder, would bear directly or indirectly. The table reflects leverage attributable to floating-rate notes for the fiscal year ended March 31, 2023 in an amount equal to 11.09% of the Fund's average gross assets (including floating-rate notes) and shows Fund expenses stated as a percentage of net assets attributable to common shares, and not as a percentage of total assets.

Basis of Transaction Fees, Note [Text Block]

as a percentage of offering price

Other Transaction Fees, Note [Text Block]

Eaton Vance Management (“EVM”) will pay the expenses of the offering (other than the applicable commissions); therefore, offering expenses are not included in the Summary of Fund Expenses. Offering expenses generally include, but are not limited to, the preparation, review and filing with the SEC of the Trust’s registration statement (including its current Prospectus Supplement, the accompanying Prospectus and Statement of Additional Information (“SAI”)), the preparation, review and filing of any associated marketing or similar materials, costs associated with the printing, mailing or other distribution of its current Prospectus Supplement, the accompanying Prospectus, SAI and/or marketing materials, associated filing fees, stock exchange listing fees, and legal and auditing fees associated with the offering.

Management Fee not based on Net Assets, Note [Text Block]

The investment adviser fee paid by the Trust to EVM is based on the average daily gross assets of the Trust, including all assets attributable to any form of investment leverage that the Trust may utilize. Accordingly, if the Trust were to increase investment leverage in the future, the investment adviser fee will increase as a percentage of net assets.

General Description of Registrant [Abstract]

Investment Objectives and Practices [Text Block]

Investment Objectives. The Fund’s primary investment objective is to provide current income exempt from federal income tax. Capital appreciation is a secondary objective.

Principal Strategies. During normal market conditions, the Fund will invest at least 80% of its gross assets in debt obligations issued by or on behalf of states, territories and possessions of the United States, including the District of Columbia, and their political subdivisions, agencies or instrumentalities, the interest on which is exempt from regular federal income tax (“municipal obligations”). For purposes of this 80% policy, municipal obligations will include investments in residual interest bonds whose interest is exempt from regular federal income tax.

During normal market conditions, at least 70% of the Fund’s investments in municipal obligations will be investment grade quality at time of investment. A municipal obligation is considered investment grade quality if it is either (i) rated within the four highest ratings categories by at least one nationally recognized statistical rating organization (a “Rating Agency”), which are those rated Baa or higher by Moody’s Investors Service, Inc. (“Moody’s”) or BBB or higher by Standard & Poor’s Ratings Services (“S&P”) or Fitch Ratings (“Fitch”), or (ii) an unrated municipal obligation that the Fund’s investment adviser considers to be of investment grade quality. If a municipal obligation is rated differently by two or more Rating Agencies, the Fund will use the higher of such ratings (the “Municipal Obligation Rating”). If a municipal obligation is insured, the Fund will use the higher of the Municipal Obligation Rating or the insurance issuer’s rating. Securities rated in the fourth highest category (i.e., Baa by Moody’s or BBB by S&P or Fitch) are considered investment grade quality, but may have speculative characteristics.

Up to 30% of the Fund’s investments in municipal obligations may be below investment grade quality at time of investment. A municipal obligation is considered below investment grade quality if it is either (i) rated below investment grade by a Rating Agency, or (ii) an unrated municipal obligation that the Fund’s investment adviser considers to be of comparable quality. Municipal obligations of below investment grade quality (commonly referred to as “junk” bonds) involve special risks as compared to municipal obligations of investment grade quality. These risks include greater sensitivity to a general economic downturn, greater market price volatility and less secondary market trading. The Fund may invest in below investment grade municipal obligations of any quality. This means that the Fund’s investments in municipal obligations may include securities of issuers that are having financial difficulties, which may include being in default on obligations to pay principal or interest thereon when due or involved in bankruptcy or insolvency proceedings (such securities are commonly referred to as “distressed securities”). The Fund generally will not invest more than 2% of its gross assets in any security of below investment grade quality. Under normal market conditions, the Fund will seek to maintain an average credit quality of investment grade.

Up to 20% of the Fund’s investments in municipal obligations may be subject to the alternative minimum tax. Up to 5% of the Fund’s investments in municipal obligations may be collateralized by the proceeds from class action or other litigation against the tobacco industry. Such municipal obligations 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. The Fund invests in residual interest bonds, also known as inverse floating rate securities, which have the economic effect of leverage. If the Fund invests 25% or more of its gross assets in any one state (or U.S. territory) the Fund may be more susceptible to adverse economic, political or regulatory occurrences affecting a particular state (or territory). The Fund generally will not invest more than 2% of its gross assets in any security of below investment grade quality.

The Fund may purchase municipal obligations 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, residual interest bonds and short-term floating-rate securities. Such municipal obligations may be acquired through investments in pooled vehicles, partnerships, or other investment companies. No established resale market exists for certain of the municipal obligations in which the Fund may invest. The Fund has no limitation on the amount of its assets that may be invested in securities that are not readily marketable or are subject to restrictions on resale.

In addition to investing in residual interest bonds, the Fund may invest without limitation in other derivative instruments (which are instruments that derive their value from another instrument, security or index) acquired for hedging purposes. The Fund may purchase and sell various kinds of financial futures contracts and related options, including futures contracts and related options based on various debt securities and securities indices. The Fund also may enter into interest rate, total return and other swaps and forward rate contracts to seek to hedge against changes in interest rates or for other risk management purposes.

During unusual market conditions, the Fund may invest up to 100% of its assets in cash or cash equivalents temporarily, which may be inconsistent with its investment objective(s) and other policies.

Risk Factors [Table Text Block]

Principal Risks

Market Discount Risk. As with any security, the market value of the common shares may increase or decrease from the amount initially paid for the common shares. The Fund’s common shares have traded both at a premium and at a discount relative to NAV. The shares of closed-end management investment companies frequently trade at a discount from their NAV. This is a risk separate and distinct from the risk that the Fund’s NAV may decrease.

Market Risk. The value of investments held by the Fund may increase or decrease in response to social, economic, political, financial, public health crises or other disruptive events (whether real, expected or perceived) in the U.S. and global markets and include events such as war, natural disasters, epidemics and pandemics, terrorism, conflicts and social unrest. These events may negatively impact broad segments of businesses and populations and may exacerbate pre-existing risks to the Fund. The frequency and magnitude of such resulting changes in the value of the Fund’s investments cannot be predicted. Certain securities and other investments held by the Fund may experience increased volatility, illiquidity, or other potentially adverse effects in

reaction to changing market conditions. Monetary and/or fiscal actions taken by U.S. or foreign governments to stimulate or stabilize the global economy may not be effective and could lead to high market volatility. No active trading market may exist for certain investments held by the Fund, which may impair the ability of the Fund to sell or to realize the current valuation of such investments in the event of the need to liquidate such assets.

Municipal Obligations Risk. The amount of public information available about municipal obligations is generally less than for corporate equities or bonds, meaning that the investment performance of municipal obligations may be more dependent on the analytical abilities of the investment adviser than stock or corporate bond investments. The secondary market for municipal obligations also tends to be less well-developed and less liquid than many other securities markets, which may limit the Fund’s ability to sell its municipal obligations at attractive prices. The differences between the price at which an obligation can be purchased and the price at which it can be sold may widen during periods of market distress. Less liquid obligations can become more difficult to value and be subject to erratic price movements. The increased presence of nontraditional participants (such as proprietary trading desks of investment banks and hedge funds) or the absence of traditional participants (such as individuals, insurance companies, banks and life insurance companies) in the municipal markets may lead to greater volatility in the markets because non-traditional participants may trade more frequently or in greater volume.

Interest Rate Risk. In general, the value of debt instruments will fluctuate based on changes in interest rates. The value of these securities is likely to increase when interest rates fall and decline when interest rates rise. Duration measures the time-weighted expected cash flows of a fixed-income security, while maturity refers to the amount of time until a fixed-income security matures. Generally, securities with longer durations or maturities are more sensitive to changes in interest rates than securities with shorter durations or maturities, causing them to be more volatile. Conversely, fixed-income securities with shorter durations or maturities will be less volatile but may provide lower returns than fixed-income securities with longer durations or maturities. Because the Fund is managed toward an income objective, it may hold more longer-duration or maturity obligations and thereby be more exposed to interest rate risk than municipal income funds that are managed with a greater emphasis on total return. The impact of interest rate changes is significantly less for floating-rate instruments that have relatively short periodic rate resets (e.g., ninety days or less). In a rising interest rate environment, the durations or maturities of income securities that have the ability to be prepaid or called by the issuer may be extended. In a declining interest rate environment, the proceeds from prepaid or maturing instruments may have to be reinvested at a lower interest rate. Certain instruments held by the Fund may pay an interest rate based on the London Interbank Offered Rate (“LIBOR”), which is the average offered rate for various maturities of short-term loans between certain major international banks. LIBOR is used throughout global banking and financial industries to determine interest rates for a variety of financial instruments (such as debt instruments and derivatives) and borrowing arrangements. The ICE Benchmark Administration Limited, the administrator of LIBOR, ceased publishing certain LIBOR settings on December 31, 2021, and is expected to cease the remaining LIBOR settings on June 30, 2023. Although the transition process away from LIBOR has become increasingly well defined, the impact on certain debt securities, derivatives and other financial instruments that utilize LIBOR remains uncertain. The phase-out of LIBOR may result in, among other things, increased volatility or illiquidity in markets for instruments based on LIBOR and changes in the value of such instruments.

Credit Risk. Investments in municipal obligations and other debt obligations (referred to below as “debt instruments”) are subject to the risk of non-payment of scheduled principal and interest. Changes in economic conditions or other circumstances may reduce the capacity of the party obligated to make principal and interest payments on such instruments and may lead to defaults. Such non-payments and defaults may reduce the value of Fund shares and income distributions. The value of debt instruments also may decline because of concerns about the issuer’s ability to make principal and interest payments. In addition, the credit ratings of debt instruments may be lowered if the financial condition of the party obligated to make payments with respect to such instruments deteriorates. In order to enforce its rights in the event of a default, bankruptcy or similar situation, the Fund may be required to retain legal or similar counsel, which may increase the Fund’s operating expenses and adversely affect net asset value. Municipal obligations may be insured as to principal and interest payments. If the claims-paying ability or other rating of the insurer is downgraded by a rating agency, the value of such obligations may be negatively affected.

Lower Rated Investments Risk. Investments rated below investment grade and comparable unrated investments (sometimes referred to as “junk”) have speculative characteristics because of the credit risk associated with their issuers. Changes in economic conditions or other circumstances typically have a greater effect on the ability of issuers of lower rated investments to make principal and interest payments than they do on issuers of higher rated investments. An economic downturn generally leads to a higher non-payment rate, and a lower rated investment may lose significant value before a default occurs. Lower rated investments typically are subject to greater price volatility and illiquidity than higher rated investments.

Leverage Risk. Certain Fund transactions may give rise to leverage. Leverage can result from a non-cash exposure to an underlying reference instrument. Leverage can also result from borrowings, issuance of preferred shares or participation in residual interest bond transactions. Leverage can increase both the risk and return potential of the Fund. The use of leverage may cause the Fund to maintain liquid assets or liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet segregation requirements. Leverage may cause the Fund’s NAV to be more volatile than if it had not been leveraged, as certain types of leverage may exaggerate the effect of any increase or decrease in the Fund’s portfolio securities. The loss on leveraged investments may substantially exceed the initial investment.

Risk of Residual Interest Bonds. The Fund may enter into residual interest bond transactions, which expose the Fund to leverage and greater risk than an investment in a fixed-rate municipal bond. The interest payments that the Fund receives on the residual interest bonds acquired in such transactions vary inversely with short-term interest rates, normally decreasing when short-term rates increase. The value and market for residual interest bonds are volatile and such bonds may have limited liquidity. As required by applicable accounting standards, the Fund records interest expense on its liability with respect to floating-rate notes and also records offsetting interest income in an amount equal to this expense.

Restricted Securities Risk. Unless registered for sale to the public under applicable federal securities law, restricted securities can be sold only in private transactions to qualified purchasers pursuant to an exemption from registration. The sale price realized from a private transaction could be less than the Fund’s purchase price for the restricted security. It may be difficult to identify a qualified purchaser for a restricted security held by the Fund and such security could be deemed illiquid. It may also be more difficult to value such securities.

Derivatives Risk. The Fund’s exposure to derivatives involves risks different from, or possibly greater than, the risks associated with investing directly in securities and other investments. The use of derivatives can lead to losses because of adverse movements in the price or value of the security, instrument, index, currency, commodity, economic indicator or event underlying a derivative (“reference instrument”), due to failure of a counterparty or due to tax or regulatory constraints. Derivatives may create leverage in the Fund, which represents a non-cash exposure to the underlying reference instrument. Leverage can increase both the risk and return potential of the Fund. Derivatives risk may be more significant when derivatives are used to enhance return or as a substitute for a cash investment position, rather than solely to hedge the risk of a position held by the Fund. Use of derivatives involves the exercise of specialized skill and judgment, and a transaction may be unsuccessful in whole or in part because of market behavior or unexpected events. Changes in the value of a derivative (including one used for hedging) may not correlate perfectly with the underlying reference instrument. Derivative instruments traded in over-the-counter markets may be difficult to value, may be illiquid, and may be subject to wide swings in valuation caused by changes in the value of the underlying reference instrument. If a derivative’s counterparty is unable to honor its commitments, the value of Fund shares may decline and the Fund could experience delays in (or be unable to achieve) the return of collateral or other assets held by the counterparty. The loss on derivative transactions may substantially exceed the initial investment. A derivative investment also involves the risks relating to the reference instrument underlying the investment.

Liquidity Risk. The Fund is exposed to liquidity risk when trading volume, lack of a market maker or trading partner, large position size, market conditions, or legal restrictions impair its ability to sell particular investments or to sell them at advantageous market prices. Consequently, the Fund may have to accept a lower price to sell an investment or continue to hold it or keep the position open, sell other investments to raise cash or abandon an investment opportunity, any of which could have a negative effect on the Fund’s performance. These effects may be exacerbated during times of financial or political stress.

Sector and Geographic Risk. Because the Fund may invest a significant portion of its assets in obligations issued in a particular state and/or U.S. territories and in certain types of municipal or other obligations and/or in certain sectors, the value of Fund shares may be affected by events that adversely affect that state, U.S. territory, sector or type of obligation and may fluctuate more than that of a fund that invests more broadly. General obligation bonds issued by municipalities are adversely affected by economic downturns and any resulting decline in tax revenues.

Recent Market Conditions. The outbreak of COVID-19 and efforts to contain its spread resulted in closing borders, enhanced health screenings, changes to healthcare service preparation and delivery, quarantines, cancellations, disruptions to supply chains and customer activity, as well as general concern and uncertainty. The impact of this coronavirus, and the effects of other infectious illness outbreaks, epidemics or pandemics, may be short term continue for an extended period of time. Health crises caused by outbreaks of disease, such as the coronavirus outbreak, may exacerbate other pre-existing political, social and economic risks and disrupt normal market conditions and operations. For example, a global pandemic or other widespread health crisis could cause substantial market volatility and exchange trading suspensions and closures. In addition, the increasing interconnectedness of markets around the world may result in many markets being affected by events or conditions in a single country or region or events affecting a single or small number of issuers. The coronavirus outbreak and public and private sector responses thereto have led to large portions of the populations of many countries working from home for indefinite periods of time, temporary or permanent layoffs, disruptions in supply chains, and lack of availability of certain goods. The impact of such responses could adversely affect the information technology and operational systems upon which the Fund and the Fund’s service providers rely, and could otherwise disrupt the ability of the employees of the Fund’s service providers to perform critical tasks relating to the Fund. Any such impact could adversely affect the Fund’s performance, or the performance of the securities in which the Fund invests and may lead to losses on your investment in the Fund.

Risks Associated with Active Management. The success of the Fund’s investment strategy depends on portfolio management’s successful application of analytical skills and investment judgment. Active management involves subjective decisions and there is no guarantee that such decisions will produce the desired results or expected returns.

Tax Risk. Income from tax-exempt municipal obligations could be declared taxable because of changes in tax laws, adverse interpretations by the relevant taxing authority or the non-compliant conduct of the issuer of an obligation.

Tax-Sensitive Investing Risk. The Fund may hold a security in order to achieve more favorable tax-treatment or to sell a security in order to create tax losses. The Fund’s utilization of various tax-management techniques may be curtailed or eliminated by tax legislation, regulation or interpretations. The Fund may not be able to minimize taxable distributions to shareholders and a portion of the Fund’s distributions may be taxable.

Cybersecurity Risk. With the increased use of technologies by Fund service providers to conduct business, such as the Internet, the Fund is susceptible to operational, information security and related risks. In general, cyber incidents can result from deliberate attacks or unintentional events. Cybersecurity failures by or breaches of the Fund’s investment adviser or administrator and other service providers (including, but not limited to, the custodian or transfer agent), and the issuers of securities in which the Fund invests, may disrupt and otherwise adversely affect their business operations. This may result in

financial losses to the Fund, impede Fund trading, interfere with the Fund’s ability to calculate its net asset value, interfere with Fund shareholders’ ability to transact business or cause violations of applicable privacy and other laws, regulatory fines, penalties, reputational damage, reimbursement or other compensation costs, or additional compliance costs.

General Fund Investing Risks. The Fund is not a complete investment program and there is no guarantee that the Fund will achieve its investment objective. It is possible to lose money by investing in the Fund. An investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Share Price [Table Text Block]

The following table sets forth for each of the periods indicated the high and low closing market prices for the common shares on the New York Stock Exchange, and the corresponding NAV per share and the premium or discount to NAV per share at which the Trust’s common shares were trading as of such date.

	Market Price ($)		NAV per Share on Date of Market Price ($)		NAV Premium/(Discount) on Date of Market Price (%)
Fiscal Quarter Ended	High	Low	High	Low	High	Low
March 31, 2023	18.03	16.48	18.47	17.93	(2.38)	(8.09)
December 31, 2022	17.95	15.53	18.23	16.87	(1.54)	(7.94)
September 30, 2022	19.19	16.12	18.93	17.45	1.37	(7.62)
June 30, 2022	18.93	16.38	20.07	18.32	(5.68)	(10.59)
March 31, 2022	22.17	18.78	21.99	20.01	0.82	(6.15)
December 31, 2021	24.00	22.07	22.08	21.99	8.70	0.36
September 30, 2021	24.09	22.23	22.48	22.27	7.16	(0.18)
June 30, 2021	23.45	22.09	22.11	22.23	6.06	(0.63)