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BlackRock Short Maturity Municipal Bond ETF  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading BLACKROCK® SHORT MATURITY MUNICIPAL BOND ETF Ticker: MEAR Stock Exchange: Cboe BZX
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The BlackRock Short Maturity Municipal Bond ETF (the “Fund”) seeks to maximize tax-free current income.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses that you will incur if you buy, hold and sell shares of the Fund. The investment advisory agreement between iShares U.S. ETF Trust (the “Trust”) and BlackRock Fund Advisors (“BFA”) (the “Investment Advisory Agreement”) provides that BFA will pay all operating expenses of the Fund, except: (i) the management fees, (ii) interest expenses, (iii) taxes, (iv) expenses incurred with respect to the acquisition and disposition of portfolio securities and the execution of portfolio transactions, including brokerage commissions, (v) distribution fees or expenses, and (vi) litigation expenses and extraordinary expenses.
You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investments)1
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The Fund may pay transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in the Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 195% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 195.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This Example is intended to help you compare the cost of owning shares of the Fund with the cost of investing in other funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then sell all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The Fund seeks to achieve its investment objective by investing, under normal circumstances, at least 80% of its net assets in municipal securities such that the interest on each bond is exempt from U.S. federal income taxes and the federal alternative minimum tax (“AMT”). Under normal circumstances, the Fund primarily invests in U.S. dollar-denominated, investment-grade short-term fixed- and floating-rate municipal securities with remaining maturities of five years or less, such as municipal bonds, municipal notes and variable rate demand obligations, as well as money market instruments and registered investment companies. Investment-grade securities are rated BBB- or higher by S&P Global Ratings and/or Fitch Ratings, Inc. (“Fitch”), or Baa3 or higher by Moody’s Investors Service, Inc. (“Moody's”), or, if unrated, determined by the Fund's management team to be of equivalent quality. Municipal bonds include debt obligations issued by or on behalf of a governmental entity or other qualifying issuer that pay interest that is, in the
opinion of bond counsel to the issuer at the time of issuance, generally excludable from gross income for U.S. federal income tax purposes. The Fund may invest up to 20% of its net assets in municipal securities that pay interest that is subject to the federal AMT. Issuers may be states, territories and possessions of the U.S., including the District of Columbia, and their political subdivisions, agencies and instrumentalities. BFA or its affiliates may advise the money market funds and investment companies in which the Fund may invest.
Under normal circumstances, the effective duration of the Fund's portfolio is expected to be 1.2 years or less, as calculated by the Fund's management team, and it is not expected to exceed 1.5 years. Effective duration is a measure of the Fund’s price sensitivity to changes in yields or interest rates; however, investors should be aware that effective duration is not an exact measurement and may not reliably predict a particular security’s price sensitivity to changes in yield or interest rates.
Under normal circumstances, the Fund will also seek to maintain a weighted average maturity that is less than three years. Weighted average maturity is a U.S. dollar-weighted average of the remaining term to maturity of the underlying securities in the Fund’s portfolio. The calculation of the Fund's weighted average maturity is based on the constituent securities' final maturity date or, for amortizing securities such as asset-backed and mortgage-backed securities, their weighted average life (i.e., the average length of time that each dollar of unpaid principal on the security remains outstanding).
The Fund is an actively managed exchange-traded fund (“ETF”) that does not seek to replicate the performance of a specified index. The Fund may have a higher degree of portfolio turnover than funds that seek to replicate the performance of an index.
The Fund is not a money market fund and does not seek to maintain a stable net asset value of $1.00 per share. Please see the Fund’s Statement of Additional Information (“SAI”) for further information.
Risk [Heading] rr_RiskHeading Summary of Principal Risks
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The bar chart and table that follow show how the Fund has performed on a calendar year basis and provide some indication of the risks of investing in the Fund by showing how the Fund’s average annual returns for 1 and 5 years and since inception compare with those of a broad measure of market performance. Both assume that all dividends and distributions have been reinvested in the Fund. Past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future. If BFA had not waived certain Fund fees during certain periods, the Fund's returns would have been lower.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table that follow show how the Fund has performed on a calendar year basis and provide some indication of the risks of investing in the Fund by showing how the Fund’s average annual returns for 1 and 5 years and since inception compare with those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-iShares (1-800-474-2737) (toll free)
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.iShares.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) does not necessarily indicate how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year by Year Returns 
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
The best calendar quarter return during the periods shown above was 1.60% in the 4th quarter of 2023; the worst was -0.67% in the 1st quarter of 2022.
Updated performance information, including the Fund’s current NAV, may be obtained by visiting our website at www.iShares.com or by calling 1-800-iShares (1-800-474-2737) (toll free).
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2023) 
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns in the table above are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state or local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown, and after-tax returns shown are not relevant to tax-exempt investors or investors who hold shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”).
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher Fund returns after taxes on distributions and sales of Fund shares are calculated assuming that an investor has sufficient capital gains of the same character from other investments to offset any capital losses from the sale of Fund shares. As a result, Fund returns after taxes on distributions and sales of Fund shares may exceed Fund returns before taxes and/or returns after taxes on distributions.
BlackRock Short Maturity Municipal Bond ETF | Risk Lose Money [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock As with any investment, you could lose all or part of your investment in the Fund, and the Fund's performance could trail that of other investments.
BlackRock Short Maturity Municipal Bond ETF | Municipal Securities Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Municipal Securities Risk. Municipal securities can be significantly affected by political or economic changes, including changes made in the law after issuance of the securities, as well as uncertainties in the municipal market related to taxation, legislative changes or the rights of municipal security holders, including in connection with an issuer insolvency. Municipal securities backed by current or anticipated revenues from a specific project or specific assets can be negatively affected by the inability to collect
revenues from such projects or assets. Certain municipal securities are issued by entities with limited taxing authority such as school districts, or are dependent on revenue from a particular sector or industry, such as the utilities sector, infrastructure sector, or transportation industry.
BlackRock Short Maturity Municipal Bond ETF | Credit Risks [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Credit Risk. Debt issuers and other counterparties may be unable or unwilling to make timely interest and/or principal payments when due or otherwise honor their obligations. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also adversely affect the value of the Fund’s investment in that issuer. The degree of credit risk depends on an issuer's or counterparty's financial condition and on the terms of an obligation.
BlackRock Short Maturity Municipal Bond ETF | Interest Rate Risks [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Interest Rate Risk. During periods of very low or negative interest rates, the Fund may be unable to maintain positive returns or pay dividends to Fund shareholders. Very low or negative interest rates may magnify interest rate risk. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, result in heightened market volatility and detract from the Fund’s performance to the extent the Fund is exposed to such interest rates. Additionally, under certain market conditions in which interest rates are low and the market prices for portfolio securities have increased, the Fund may have a very low or even negative yield. A low or negative yield would cause the Fund to lose money in certain conditions and over certain time periods. An increase in interest rates will generally cause the value of securities held by the Fund to decline, may lead to heightened volatility in the fixed-income markets
and may adversely affect the liquidity of certain fixed-income investments, including those held by the Fund. Because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities. The historically low interest rate environment in recent years heightens the risks associated with rising interest rates.
BlackRock Short Maturity Municipal Bond ETF | Risk of Investing in the US [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Risk of Investing in the U.S. Certain changes in the U.S. economy, such as when the U.S. economy weakens or when its financial markets decline, may have an adverse effect on the securities to which the Fund has exposure.
BlackRock Short Maturity Municipal Bond ETF | Market Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Market Risk. The Fund could lose money over short periods due to short-term market movements and over longer periods during more prolonged market downturns. Local, regional or global events such as war, acts of terrorism, public health issues, recessions, the prospect or occurrence of a sovereign default or other financial crisis, or other events could have a significant impact on the Fund and its investments and could result in increased premiums or discounts to the Fund’s NAV.
BlackRock Short Maturity Municipal Bond ETF | Management Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Management Risk. The Fund is subject to management risk, which is the risk that the investment process, techniques and risk analyses applied by BFA will not produce the desired results, and that securities selected by BFA may underperform the market or any relevant benchmark. In addition, legislative, regulatory, or tax developments may affect the
investment techniques available to BFA in connection with managing the Fund and may also adversely affect the ability of the Fund to achieve its investment objective.
BlackRock Short Maturity Municipal Bond ETF | Asset Class Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Asset Class Risk. Securities and other assets in the Fund's portfolio may underperform in comparison to the general financial markets, a particular financial market or other asset classes.
BlackRock Short Maturity Municipal Bond ETF | Authorized Participant Concentration Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Authorized Participant Concentration Risk. Only an Authorized Participant (as defined in the Creations and Redemptions section of this prospectus (the “Prospectus”)) may engage in creation or redemption transactions directly with the Fund, and none of those Authorized Participants is obligated to engage in creation and/or redemption transactions. The Fund has a limited number of institutions that may act as Authorized Participants on an agency basis (i.e., on behalf of other market participants). To the extent that Authorized Participants exit the business or are unable to proceed with creation or redemption orders with respect to the Fund and no other Authorized Participant is able to step forward to create or redeem, Fund shares may be more likely to trade at a premium or discount to NAV and possibly face trading halts or delisting.
BlackRock Short Maturity Municipal Bond ETF | Call Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Call Risk. During periods of falling interest rates, an issuer of a callable bond held by the Fund may “call” or repay the security before its stated maturity, and the Fund may have to reinvest the proceeds in securities with lower yields, which would result in a decline in the Fund's income, or in securities with greater risks or with other less favorable features.
BlackRock Short Maturity Municipal Bond ETF | Cash Transactions Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Cash Transactions Risk. The Fund may effect part or all of its creations and
redemptions for cash, rather than in-kind securities. As a result, the Fund may have to sell portfolio securities at inopportune times in order to obtain the cash needed to meet redemption orders. This may cause the Fund to sell a security and recognize a capital gain or loss that might not have been incurred if it had made a redemption in-kind. The use of cash creations and redemptions may also cause the Fund’s shares to trade in the market at wider bid-ask spreads or greater premiums or discounts to the Fund’s NAV.
BlackRock Short Maturity Municipal Bond ETF | Concentration Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Concentration Risk. The Fund may be susceptible to an increased risk of loss, including losses due to adverse events that affect the Fund’s investments more than the market as a whole, to the extent that the Fund's investments are concentrated in the securities and/or other assets of a particular issuer or issuers, country, group of countries, region, market, industry, group of industries, sector, market segment or asset class.
BlackRock Short Maturity Municipal Bond ETF | Cybersecurity Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Cybersecurity Risk. Failures or breaches of the electronic systems of the Fund, the Fund's adviser, distributor, and other service providers (including the benchmark provider), market makers, Authorized Participants or the issuers of securities in which the Fund invests have the ability to cause disruptions, negatively impact the Fund’s business operations and/or potentially result in financial losses to the Fund and its shareholders. While the Fund has established business continuity plans and risk management systems seeking to address system breaches or failures, there are inherent limitations in such plans and systems. Furthermore, the Fund cannot control the cybersecurity plans and systems of the Fund’s service providers, market
makers, Authorized Participants or issuers of securities in which the Fund invests.
BlackRock Short Maturity Municipal Bond ETF | Floating Rate Securities Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Floating Rate Securities Risk. Securities with floating or variable interest rates can be less sensitive to interest rate changes than securities with fixed interest rates, but may decline in value if their coupon rates do not reset as high, or as quickly, as comparable market interest rates, and generally carry lower yields than fixed securities of the same maturity. Although floating rate securities are less sensitive to interest rate risk than fixed-rate securities, they are subject to credit risk and default risk, which could impair their value.
BlackRock Short Maturity Municipal Bond ETF | High Portfolio Turnover Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
High Portfolio Turnover Risk. The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (considered by the Fund to mean higher than 100% annually) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities.
BlackRock Short Maturity Municipal Bond ETF | Illiquid Investments Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Illiquid Investments Risk. The Fund may not acquire any illiquid investment if, immediately after the acquisition, the Fund would have invested more than 15% of its net assets in illiquid investments. An illiquid investment is any investment that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without significantly changing the market value of the investment. To the extent the Fund holds illiquid investments, the illiquid investments may reduce the returns of the Fund because the Fund may be unable to
transact at advantageous times or prices. In addition, if the Fund is limited in its ability to sell illiquid investments during periods when shareholders are redeeming their shares, the Fund will need to sell liquid securities to meet redemption requests and illiquid securities will become a larger portion of the Fund’s holdings. During periods of market volatility, liquidity in the market for the Fund’s shares may be impacted by the liquidity in the market for the underlying securities or instruments held by the Fund, which could lead to the Fund’s shares trading at a premium or discount to the Fund’s NAV.
BlackRock Short Maturity Municipal Bond ETF | Income Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Income Risk. The Fund’s income may decline when interest rates fall because the Fund may hold a significant portion of short duration securities and/or securities that have floating or variable interest rates. The Fund’s income may decline because the Fund invests in lower yielding bonds, and as the bonds in its portfolio mature, are near maturity or are called, the Fund needs to purchase additional bonds.
BlackRock Short Maturity Municipal Bond ETF | Infectious Illness Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Infectious Illness Risk. A widespread outbreak of an infectious illness, such as the COVID-19 pandemic, may result in travel restrictions, disruption of healthcare services, prolonged quarantines, cancellations, supply chain disruptions, business closures, lower consumer demand, layoffs, ratings downgrades, defaults and other significant economic, social and political impacts. Markets may experience temporary closures, extreme volatility, severe losses, reduced liquidity and increased trading costs. Such events may adversely affect the Fund and its investments and may impact the Fund’s ability to purchase or sell securities or cause elevated tracking error and increased premiums or discounts to the
Fund's NAV. Despite the development of vaccines, the duration of the COVID-19 pandemic and its effects cannot be predicted with certainty.
BlackRock Short Maturity Municipal Bond ETF | Issuer Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Issuer Risk. The performance of the Fund depends on the performance of individual securities to which the Fund has exposure. The Fund may be adversely affected if an issuer of underlying securities held by the Fund is unable or unwilling to repay principal or interest when due. Changes in the financial condition or credit rating of an issuer of those securities may cause the value of the securities to decline.
BlackRock Short Maturity Municipal Bond ETF | Large Shareholder and Large Scale Redemption Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Large Shareholder and Large-Scale Redemption Risk. Certain shareholders, including an Authorized Participant, a third-party investor, the Fund’s adviser or an affiliate of the Fund’s adviser, a market maker, or another entity, may from time to time own or manage a substantial amount of Fund shares, or may invest in the Fund and hold their investment for a limited period of time. There can be no assurance that any large shareholder or large group of shareholders would not redeem their investment. Redemptions of a large number of Fund shares could require the Fund to dispose of assets to meet the redemption requests, which can accelerate the realization of taxable income and/or capital gains and cause the Fund to make taxable distributions to its shareholders earlier than the Fund otherwise would have. In addition, under certain circumstances, non-redeeming shareholders may be treated as receiving a disproportionately large taxable distribution during or with respect to such year. In some circumstances, the Fund may hold a relatively large proportion of its assets in cash in anticipation of large redemptions, diluting its investment
returns. These large redemptions may also force the Fund to sell portfolio securities when it might not otherwise do so, which may negatively impact the Fund’s NAV, increase the Fund’s brokerage costs and/or have a material effect on the market price of the Fund shares.
BlackRock Short Maturity Municipal Bond ETF | Market Trading Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Market Trading Risk. The Fund faces numerous market trading risks, including the potential lack of an active market for Fund shares, losses from trading in secondary markets, periods of high volatility and disruptions in the creation/redemption process. Unlike some ETFs that track specific indexes, the Fund does not seek to replicate the performance of a specified index. Index-based ETFs have generally traded at prices that closely correspond to NAV. However, ETFs that do not seek to replicate the performance of a specified index have a limited trading history and, therefore, there can be no assurance as to whether, and/or the extent to which, the Fund's shares will trade at premiums or discounts to NAV. ANY OF THESE FACTORS, AMONG OTHERS, MAY LEAD TO THE FUND'S SHARES TRADING AT A PREMIUM OR DISCOUNT TO NAV.
BlackRock Short Maturity Municipal Bond ETF | Not a Money Market Fund [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Not a Money Market Fund. The Fund is not a money market fund and is not subject to the strict rules that govern the quality, maturity, liquidity and other features of securities that money market funds may purchase. Under normal circumstances, the Fund’s investments may be more susceptible than a money market fund is to credit risk, interest rate risk, valuation risk and other risks relevant to the Fund’s investments. The Fund does not seek to maintain a stable net asset value of $1.00 per share.
BlackRock Short Maturity Municipal Bond ETF | Operational Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Operational Risk. The Fund is exposed to operational risks arising from a number of factors, including, but not limited to, human error, processing and communication errors, errors of the Fund’s service providers, counterparties or other third parties, failed or inadequate processes and technology or systems failures. The Fund and BFA seek to reduce these operational risks through controls and procedures. However, these measures do not address every possible risk and may be inadequate to address significant operational risks.
BlackRock Short Maturity Municipal Bond ETF | Tax Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Tax Risk. There is no guarantee that the Fund's income will be exempt from U.S. federal income taxes, the federal AMT or the federal Medicare contribution tax of 3.8% on “net investment income.”
BlackRock Short Maturity Municipal Bond ETF | Valuation Risk [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock
Valuation Risk. The price the Fund could receive upon the sale of a security or other asset may differ from the Fund's valuation of the security or other asset, particularly for securities or other assets that trade in low volume or volatile markets or that are valued using a fair value methodology as a result of trade suspensions or for other reasons. In addition, the value of the securities or other assets in the Fund's portfolio may change on days or during time periods when shareholders will not be able to purchase or sell the Fund's shares. Authorized Participants who purchase or redeem Fund shares on days when the Fund is holding fair-valued securities may receive fewer or more shares, or lower or higher redemption proceeds, than they would have received had the securities not been fair valued or been valued using a different methodology. The ability to value investments may be impacted by technological issues or errors by pricing services or other third-party service providers.
BlackRock Short Maturity Municipal Bond ETF | BlackRock Short Maturity Municipal Bond ETF  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.25% [1]
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none [1]
Other Expenses rr_OtherExpensesOverAssets none [1],[2]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.25% [1]
1 Year rr_ExpenseExampleYear01 $ 26
3 Years rr_ExpenseExampleYear03 80
5 Years rr_ExpenseExampleYear05 141
10 Years rr_ExpenseExampleYear10 $ 318
2016 rr_AnnualReturn2016 0.59%
2017 rr_AnnualReturn2017 0.97%
2018 rr_AnnualReturn2018 1.58%
2019 rr_AnnualReturn2019 2.03%
2020 rr_AnnualReturn2020 1.11%
2021 rr_AnnualReturn2021 0.06%
2022 rr_AnnualReturn2022 0.15%
2023 rr_AnnualReturn2023 3.96%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel best
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2023
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.60%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel worst
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2022
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (0.67%)
One Year rr_AverageAnnualReturnYear01 3.96%
Five Years rr_AverageAnnualReturnYear05 1.45%
Since Inception rr_AverageAnnualReturnSinceInception 1.22%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 03, 2015
BlackRock Short Maturity Municipal Bond ETF | Return After Taxes on Distributions | BlackRock Short Maturity Municipal Bond ETF  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 3.96% [3]
Five Years rr_AverageAnnualReturnYear05 1.45% [3]
Since Inception rr_AverageAnnualReturnSinceInception 1.22% [3]
BlackRock Short Maturity Municipal Bond ETF | Return After Taxes on Distributions and Sale of Fund Shares | BlackRock Short Maturity Municipal Bond ETF  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 3.72% [3]
Five Years rr_AverageAnnualReturnYear05 1.44% [3]
Since Inception rr_AverageAnnualReturnSinceInception 1.22% [3]
BlackRock Short Maturity Municipal Bond ETF | Bloomberg Municipal Bond: 1 Year (1-2) Index (Index returns do not reflect deductions for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 2.90% [4]
Five Years rr_AverageAnnualReturnYear05 1.25% [4]
Since Inception rr_AverageAnnualReturnSinceInception 1.08% [4]
[1] Operating expenses paid by BFA under the Investment Advisory Agreement exclude acquired fund fees and expenses, if any.
[2] The amount rounded to 0.00%.
[3] After-tax returns in the table above are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state or local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown, and after-tax returns shown are not relevant to tax-exempt investors or investors who hold shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts (“IRAs”). Fund returns after taxes on distributions and sales of Fund shares are calculated assuming that an investor has sufficient capital gains of the same character from other investments to offset any capital losses from the sale of Fund shares. As a result, Fund returns after taxes on distributions and sales of Fund shares may exceed Fund returns before taxes and/or returns after taxes on distributions.
[4] The Bloomberg Municipal Bond: 1 Year (1-2) Index is an unmanaged index comprised of national municipal bond issues having a maturity of at least one year and less than two years.