Investor A1 [Member] Performance Management - Investor A1 - BlackRock Strategic Municipal Opportunities Fund |
May 31, 2025 |
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| Prospectus [Line Items] | |
| Bar Chart and Performance Table [Heading] | Performance Information |
| Performance Narrative [Text Block] | The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the Bloomberg Municipal Bond Index and a customized weighted index comprised of the Bloomberg Municipal Bond Index Total Return Index Value Unhedged (75%), the Bloomberg Municipal Bond: High Yield (non-Investment Grade) Total Return Index (20%), and the Bloomberg Municipal Index Taxable Bonds Total Return Index Value (5%) (the “Customized Reference Benchmark”). The Customized Reference Benchmark is relevant to the Fund because it has characteristics similar to the Fund’s investment strategy. To the extent that dividends and distributions have been paid by the Fund, the performance information for the Fund in the chart and table assumes reinvestment of the dividends and distributions. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance, including its current net asset value, can be obtained by visiting http://www.blackrock.com or can be obtained by phone at 800-882-0052.
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| Performance Past Does Not Indicate Future [Text] | As with allsuch investments, past performance (before and after taxes) is not an indication of future results. |
| Performance Information Illustrates Variability of Returns [Text] | The information shows you how the Fund’s performance has varied year by year and provides some indication of therisks of investing in the Fund. |
| Performance Additional Market Index [Text] | The table compares the Fund’s performance to that of the Bloomberg Municipal BondIndex and a customized weighted index comprised of the Bloomberg Municipal Bond Index Total Return Index ValueUnhedged (75%), the Bloomberg Municipal Bond: High Yield (non-Investment Grade) Total Return Index (20%), and theBloomberg Municipal Index Taxable Bonds Total Return Index Value (5%) (the“Customized Reference Benchmark”). TheCustomized Reference Benchmark is relevant to the Fund because it has characteristics similar to the Fund’sinvestment strategy. |
| Bar Chart Does Not Reflect Sales Loads [Text] | Sales charges arenot reflected in the bar chart. If they were, returns would be less than those shown. |
| Bar Chart [Heading] | Investor A1 Shares ANNUAL TOTAL RETURNS BlackRock Strategic Municipal Opportunities Fund As of 12/31 |
| Bar Chart Closing [Text Block] | During the ten-year period shown in the bar chart, the highest return for a quarter was 7.66% (quarter ended December 31, 2023) and the lowest return for a quarter was -7.37% (quarter ended March 31, 2020). The year-to-date return as of June 30, 2025 was -1.40%.
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| Performance Table Heading | For the periods ended 12/31/24Average Annual Total Returns |
| Performance Table Narrative | After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
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| Performance Table Does Reflect Sales Loads | However, the table includes allapplicable fees and sales charges. |
| Performance Table Uses Highest Federal Rate | After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do notreflect the impact of state and local taxes. |
| Performance Table Not Relevant to Tax Deferred | Actual after-tax returns depend on the investor’s tax situation and maydiffer from those shown, and the after-tax returns shown are not relevant to investors who hold their shares throughtax-deferred arrangements, such as 401(k) plans or individual retirement accounts. |
| Performance Availability Website Address [Text] | http://www.blackrock.com |
| Performance Availability Phone [Text] | 800-882-0052 |
| Investor A1 Shares | |
| Prospectus [Line Items] | |
| Year to Date Return, Label [Optional Text] | year-to-date return |
| Bar Chart, Year to Date Return | (1.40%) |
| Bar Chart, Year to Date Return, Date | Jun. 30, 2025 |
| Highest Quarterly Return, Label [Optional Text] | highest return |
| Highest Quarterly Return | 7.66% |
| Highest Quarterly Return, Date | Dec. 31, 2023 |
| Lowest Quarterly Return, Label [Optional Text] | lowest return |
| Lowest Quarterly Return | (7.37%) |
| Lowest Quarterly Return, Date | Mar. 31, 2020 |