Investor A1 [Member] Investment Strategy - Investor A1 - BlackRock Strategic Municipal Opportunities Fund	May 31, 2025
Prospectus [Line Items]
Strategy [Heading]	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	Under normal circumstances, the Fund will invest at least 80% of its assets in municipal bonds. For the purposes of the foregoing 80% policy, “assets” are the Fund’s net assets, plus the amount of any borrowings for investment purposes. The Fund’s investments in derivatives will be counted toward the Fund’s 80% policy to the extent that they provide investment exposure to the securities included within that policy or to one or more market risk factors associated with such securities. Municipal bonds may be obligations of a variety of issuers including governmental entities or other qualifying issuers, the payments from which, in the opinion of bond counsel to the issuer, are excludable from gross income for Federal income tax purposes (although certain investors may be subject to a Federal alternative minimum tax on dividends attributable to the Fund’s investments in private activity bonds). Issuers may be states, territories and possessions of the United States, including the District of Columbia, and their political subdivisions, agencies and instrumentalities. Municipal bonds also include short-term tax-exempt obligations like municipal notes, variable rate demand obligations, private activity bonds and insured municipal bonds. The Fund may invest in both fixed rate and variable rate obligations. Under normal circumstances, the Fund seeks to maintain an average portfolio duration of zero to ten years. The Fund may invest in bonds of any maturity. Duration is a mathematical calculation of the average life of a bond (or bonds in a bond fund) that serves as a useful measure of its price risk. Each year of duration represents an expected 1% change in the net asset value of a bond fund for every 1% immediate change in interest rates. For example, if a bond fund has an average duration of ten years, its net asset value will fall about 10% when interest rates rise by one percentage point. Conversely, the bond fund’s net asset value will rise about 10% when interest rates fall by one percentage point. Duration, which measures price sensitivity to interest rate changes, is not necessarily equal to average maturity. The Fund is permitted to engage in transactions in certain derivatives, such as financial futures contracts and options thereon, for hedging purposes (including anticipatory hedges) or to seek to enhance returns. The Fund may also invest in other derivatives, such as indexed and inverse floating rate obligations and swap agreements, including credit default swap agreements, for hedging purposes (including anticipatory hedges) or to enhance income. Derivatives are financial instruments whose value is derived from another security or an index. The Fund may use derivative instruments to hedge its investments or to seek to enhance returns. Derivatives allow the Fund to increase or decrease its risk exposure more quickly and efficiently than other types of instruments. The Fund may invest up to 20% of its net assets in securities that are not municipal securities (including, but not limited to, taxable municipal bonds, U.S. Treasury and Government agency issues, and investment grade corporate bonds). The Fund may invest up to 50% of its net assets in non-investment grade bonds (commonly called “high yield” or “junk bonds”). Non-investment grade bonds are bonds that, at the time of acquisition, are rated in the lower rating categories of the major rating agencies (BB or lower by Standard & Poor’s or Fitch Ratings, Inc. or Ba or lower by Moody’s Investor Service, Inc.) or are determined by Fund management to be of similar quality. Split rated bonds will be considered to have the higher credit rating. Split rated bonds are bonds that receive different ratings from two or more rating agencies. The Fund may leverage its assets through the use of proceeds received through tender option bond transactions. In a tender option bond transaction, the Fund transfers municipal bonds or other municipal securities into a special purpose entity (a “TOB Trust”). A TOB Trust typically issues two classes of beneficial interests: short-term floating rate interests (“TOB Floaters”), which are sold to third party investors, and residual inverse floating rate interests (“TOB Residuals”), which are generally issued to the Fund. The Fund may invest in TOB Residuals and may also invest in TOB Floaters. The Fund will look through to the underlying municipal bond held by a TOB Trust for purposes of the Fund’s 80% policy. The Fund may also buy when-issued securities and participate in delayed delivery transactions. The Fund may engage in active and frequent trading of portfolio securities to achieve its primary investment strategies.

Under normal circumstances, the Fund will invest at least 80% of its assets in municipal bonds. For the purposes of the foregoing 80% policy, “assets” are the Fund’s net assets, plus the amount of any borrowings for investment purposes. The Fund’s investments in derivatives will be counted toward the Fund’s 80% policy to the extent that they provide investment exposure to the securities included within that policy or to one or more market risk factors associated with such securities. Municipal bonds may be obligations of a variety of issuers including governmental entities or other qualifying issuers, the payments from which, in the opinion of bond counsel to the issuer, are excludable from gross income for Federal income tax purposes (although certain investors may be subject to a Federal alternative minimum tax on dividends attributable to the Fund’s investments in private activity bonds). Issuers may be states, territories and possessions of the United States, including the District of Columbia, and their political subdivisions, agencies and instrumentalities. Municipal bonds also include short-term tax-exempt obligations like municipal notes, variable rate demand obligations, private activity bonds and insured municipal bonds. The Fund may invest in both fixed rate and variable rate obligations.

Under normal circumstances, the Fund seeks to maintain an average portfolio duration of zero to ten years. The Fund may invest in bonds of any maturity. Duration is a mathematical calculation of the average life of a bond (or bonds in a bond fund) that serves as a useful measure of its price risk. Each year of duration represents an expected 1% change in the net asset value of a bond fund for every 1% immediate change in interest rates. For example, if a bond fund has an average duration of ten years, its net asset value will fall about 10% when interest rates rise by one percentage point. Conversely, the bond fund’s net asset value will rise about 10% when interest rates fall by one percentage point. Duration, which measures price sensitivity to interest rate changes, is not necessarily equal to average maturity.

The Fund is permitted to engage in transactions in certain derivatives, such as financial futures contracts and options thereon, for hedging purposes (including anticipatory hedges) or to seek to enhance returns. The Fund may also invest in other derivatives, such as indexed and inverse floating rate obligations and swap agreements, including credit default swap agreements, for hedging purposes (including anticipatory hedges) or to enhance income. Derivatives are financial instruments whose value is derived from another security or an index. The Fund may use derivative instruments to hedge its investments or to seek to enhance returns. Derivatives allow the Fund to increase or decrease its risk exposure more quickly and efficiently than other types of instruments.

The Fund may invest up to 50% of its net assets in non-investment grade bonds (commonly called “high yield” or “junk bonds”). Non-investment grade bonds are bonds that, at the time of acquisition, are rated in the lower rating categories of the major rating agencies (BB or lower by Standard & Poor’s or Fitch Ratings, Inc. or Ba or lower by Moody’s Investor Service, Inc.) or are determined by Fund management to be of similar quality. Split rated bonds will be considered to have the higher credit rating. Split rated bonds are bonds that receive different ratings from two or more rating agencies.

purpose entity (a “TOB Trust”). A TOB Trust typically issues two classes of beneficial interests: short-term floating rate interests (“TOB Floaters”), which are sold to third party investors, and residual inverse floating rate interests (“TOB Residuals”), which are generally issued to the Fund. The Fund may invest in TOB Residuals and may also invest in TOB Floaters. The Fund will look through to the underlying municipal bond held by a TOB Trust for purposes of the Fund’s 80% policy.