Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK MUNICIPAL SERIES TRUST
Prospectus Date	rr_ProspectusDate	Jan. 27, 2014
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts about BlackRock Strategic Municipal Opportunities Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the BlackRock Strategic Municipal Opportunities Fund (the “Fund”) is to provide shareholders with a high level of income exempt from Federal income taxes.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in the BlackRock-advised fund complex. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. (“PNC”) and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” section on page 18 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-66 of the Fund’s statement of additional information.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	October 1, 2015
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in 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 17% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	17.00%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	A contingent deferred sales charge (“CDSC”) of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in the BlackRock-advised fund complex.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 100,000
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	The Total Annual Fund Operating Expenses and the Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem 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:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	You will pay the following expenses if you do not redeem your shares:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Fund will invest at least 80% of its assets in municipal bonds. 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 and variable rate demand obligations. 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 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 such as the Barclays Municipal Bond 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 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. The Fund may invest in tender option bonds and residual interest tender option bonds and may also invest in securities the return of which is inversely related to changes in an interest rate (“inverse floaters”). The Fund will look through to the underlying municipal bond held by a tender option bond trust for purposes of the Fund’s 80% policy. The Fund may engage in active and frequent trading of portfolio securities to achieve its primary investment strategies.
Risk [Heading]	rr_RiskHeading	Principal Risks of Investing in the Fund
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Risk is inherent in all investing. The value of your investment in the Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The following is a summary description of principal risks of investing in the Fund. Credit Risk — Credit risk refers to the possibility that the issuer of a security will not be able to make principal and interest payments when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. Derivatives Risk — The Fund’s use of derivatives may reduce the Fund’s returns and/or increase volatility. Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate perfectly with the overall securities markets. Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation. The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately. Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them. Derivatives also may expose the Fund to greater risk and increase its costs. Certain transactions in derivatives involve substantial leverage risk and may expose the Fund to potential losses that exceed the amount originally invested by the Fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet known and may not be known for some time. New regulation may make derivatives more costly, may limit the availability of derivatives, or may otherwise adversely affect the value or performance of derivatives. High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) 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. The sale of Fund portfolio securities may result in the realization and/or distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. These effects of higher than normal portfolio turnover may adversely affect Fund performance. Interest Rate Risk — Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall, and decrease as interest rates rise. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund’s portfolio would be expected to decrease by 10%. The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low rates. Junk Bonds Risk — Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that may cause income and principal losses for the Fund. Leverage Risk — Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet any required asset segregation requirements. Increases and decreases in the value of the Fund’s portfolio will be magnified when the Fund uses leverage. Liquidity Risk — Liquidity risk exists when particular investments are difficult to purchase or sell. The Fund’s investments in illiquid securities may reduce the returns of the Fund because it may be difficult to sell the illiquid securities at an advantageous time or price. To the extent that the Fund’s principal investment strategies involve derivatives or securities with substantial market and/or credit risk, the Fund will tend to have the greatest exposure to liquidity risk. Liquid investments may become illiquid after purchase by the Fund, particularly during periods of market turmoil. Illiquid investments may be harder to value, especially in changing markets, and if the Fund is forced to sell these investments to meet redemption requests or for other cash needs, the Fund may suffer a loss. In addition, when there is illiquidity in the market for certain securities, the Fund, due to limitations on illiquid investments, may be subject to purchase and sale restrictions. Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money. Municipal Securities Risks — Municipal securities risks include the ability of the issuer to repay the obligation, the relative lack of information about certain issuers of municipal securities, and the possibility of future legislative changes which could affect the market for and value of municipal securities. These risks include: General Obligation Bonds Risks — Timely payments depend on the issuer’s credit quality, ability to raise tax revenues and ability to maintain an adequate tax base. Revenue Bonds Risks — These payments depend on the money earned by the particular facility or class of facilities, or the amount of revenues derived from another source. Private Activity Bonds Risks — Municipalities and other public authorities issue private activity bonds to finance development of industrial facilities for use by a private enterprise. The private enterprise pays the principal and interest on the bond, and the issuer does not pledge its faith, credit and taxing power for repayment. The Fund’s investments may consist of private activity bonds that may subject certain shareholders to an alternative minimum tax. Moral Obligation Bonds Risks — Moral obligation bonds are generally issued by special purpose public authorities of a state or municipality. If the issuer is unable to meet its obligations, repayment of these bonds becomes a moral commitment, but not a legal obligation, of the state or municipality. Municipal Notes Risks — Municipal notes are shorter term municipal debt obligations. If there is a shortfall in the anticipated proceeds, the notes may not be fully repaid and the Fund may lose money. Municipal Lease Obligations Risks — In a municipal lease obligation, the issuer agrees to make payments when due on the lease obligation. Although the issuer does not pledge its unlimited taxing power for payment of the lease obligation, the lease obligation is secured by the leased property. Tax-Exempt Status Risk — The Fund and its investment manager will rely on the opinion of issuers’ bond counsel and, in the case of derivative securities, sponsors’ counsel, on the tax-exempt status of interest on municipal bonds and payments under derivative securities. Neither the Fund nor its investment manager will independently review the bases for those tax opinions, which may ultimately be determined to be incorrect and subject the Fund and its shareholders to substantial tax liabilities. Prepayment and Extension Risk — When interest rates fall, an issuer may redeem a security with call features by repaying it early, and the Fund may have to invest the proceeds in securities with lower yields. When interest rates rise, certain obligations will be paid off by the issuer more slowly than anticipated, causing the value of these obligations to fall. Taxability Risk — Investments in taxable municipal bonds, U.S. Treasury and Government agency issues, investment grade corporate bonds and taxable money market securities as well as some of the derivatives and other instruments discussed herein will cause the Fund to have taxable investment income. The Fund may also realize capital gains on the sale of its municipal bonds (and other securities it holds). These capital gains will be taxable regardless of whether they are derived from a sale of municipal bonds. Fund investments may also cause the Fund to recognize taxable ordinary income from market discount. The Fund will report distributions from taxable investment income, from market discount and from realized capital gains as taxable to Fund shareholders. In order for the Fund to be eligible to report distributions of tax-exempt interest income from tax-exempt or municipal securities as tax-exempt income to Fund shareholders, at least half of the Fund’s total assets must be invested in tax-exempt securities as of the end of each calendar quarter. If the Fund did not maintain that level of investment with respect to tax-exempt securities, the Fund would lose the ability to report distributions of tax-exempt interest income as tax-exempt income to Fund shareholders. The Fund expects to use derivatives for hedging, among other things. The Federal income tax treatment of a derivative may not be as favorable as a direct investment in an underlying asset. Derivatives may produce taxable income and taxable realized gain. Derivatives may adversely affect the timing, character and amount of income the Fund realizes from its investments. As a result, a larger portion of the Fund’s distributions may be treated as ordinary income rather than as tax-exempt income or as capital gains. In addition, certain derivatives are subject to mark-to-market or straddle provisions of the Internal Revenue Code of 1986, as amended. If such provisions are applicable, there could be an increase (or decrease) in the amount of taxable dividends paid by the Fund. In addition, the tax treatment of certain derivatives, such as swaps, is unsettled and may be subject to future legislation, regulation or administrative pronouncements issued by the Internal Revenue Service. Tender Option Bonds Risk — The Fund’s use of tender option bonds may reduce the Fund’s returns and/or increase volatility. Investments in tender option bonds expose the Fund to counterparty risk and leverage risk. An investment in tender option bonds typically will involve greater risk than an investment in a municipal fixed rate security, including the risk of loss of principal. U.S. Government Obligations Risk — Certain securities in which the Fund may invest, including securities issued by certain U.S. Government agencies and U.S. Government sponsored enterprises, are not guaranteed by the U.S. Government or supported by the full faith and credit of the United States.
Risk Lose Money [Text]	rr_RiskLoseMoney	You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	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 Fund’s Annual Total Returns prior to January 27, 2014 as reflected in the bar chart and the table are the returns of the Fund that followed different investment strategies under the name “BlackRock Intermediate Municipal Fund.” The table compares the Fund’s performance to that of the S&P Municipal Bond Index, a broad measure of performance, the S&P Intermediate Municipal Bond Index, and a customized weighted index comprised of the returns of the S&P Municipal Bond Investment Grade Index (65%), the S&P Municipal Bond High Yield Index (30%), and the Barclays Taxable Municipal: U.S. Aggregate Eligible Index (5%). One of the benchmarks against which the Fund measured its performance prior to January 27, 2014, the S&P Intermediate Municipal Bond Index, was replaced with a customized weighted index comprised of the returns of the S&P Municipal Bond Investment Grade Index (65%), the S&P Municipal Bond High Yield Index (30%), and the Barclays Taxable Municipal: U.S. Aggregate Eligible Index (5%). Fund management believes the customized weighted index is more relevant to the Fund’s new investment strategies. Prior to the Investor A and Investor C Shares inception date of October 2, 2006, the returns for Investor A and Investor C Shares are based on performance of the Fund’s Institutional Shares. The returns for Investor A and Investor C Shares, however, are adjusted to reflect the distribution and service (12b-1) fees applicable to such shares. 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/funds or can be obtained by phone at 800-882-0052.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	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.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	800-882-0052
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	http://www.blackrock.com/funds
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	As with all such investments, past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading]	rr_BarChartHeading	Institutional Shares ANNUAL TOTAL RETURNS BlackRock Strategic Municipal Opportunities Fund As of 12/31
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the ten-year period shown in the bar chart, the highest return for a quarter was 7.08% (quarter ended September 30, 2009) and the lowest return for a quarter was –4.09% (quarter ended December 31, 2010).
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/13 Average Annual Total Returns
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	However, the table includes all applicable fees and sales charges.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective January 27, 2014, the Fund replaced the S&P Intermediate Municipal Bond Index, a benchmark against which it measured performance, with a customized weighted index comprised of the returns of the S&P Municipal Bond Investment Grade Index (65%), the S&P Municipal Bond High Yield Index (30%), and the Barclays Taxable Municipal: U.S. Aggregate Eligible Index (5%). Fund management believes the customized weighted index more accurately reflects the investment strategies of the Fund.
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	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.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	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.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for Institutional Shares only, and the after-tax returns for Investor A and Investor C Shares will vary.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	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. After-tax returns are shown for Institutional Shares only, and the after-tax returns for Investor A and Investor C Shares will vary.
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	4.25%
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none	[1]
Management Fee	rr_ManagementFeesOverAssets	0.55%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Interest Expense	rr_Component1OtherExpensesOverAssets	0.03%
Miscellaneous Other Expense	rr_Component2OtherExpensesOverAssets	0.13%
Other Expenses	rr_OtherExpensesOverAssets	0.16%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.97%	[3]
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.05%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.92%	[2],[3]
1 Year	rr_ExpenseExampleYear01	515
3 Years	rr_ExpenseExampleYear03	716
5 Years	rr_ExpenseExampleYear05	934
10 Years	rr_ExpenseExampleYear10	1,560
1 Year	rr_AverageAnnualReturnYear01	(7.21%)
5 Years	rr_AverageAnnualReturnYear05	5.49%
10 Years	rr_AverageAnnualReturnYear10	3.33%
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | Investor C Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%	[4]
Management Fee	rr_ManagementFeesOverAssets	0.55%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Interest Expense	rr_Component1OtherExpensesOverAssets	0.03%
Miscellaneous Other Expense	rr_Component2OtherExpensesOverAssets	0.13%
Other Expenses	rr_OtherExpensesOverAssets	0.16%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.72%	[3]
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.05%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.67%	[2],[3]
1 Year	rr_ExpenseExampleYear01	270
3 Years	rr_ExpenseExampleYear03	537
5 Years	rr_ExpenseExampleYear05	929
10 Years	rr_ExpenseExampleYear10	2,026
1 Year	rr_ExpenseExampleNoRedemptionYear01	170
3 Years	rr_ExpenseExampleNoRedemptionYear03	537
5 Years	rr_ExpenseExampleNoRedemptionYear05	929
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,026
1 Year	rr_AverageAnnualReturnYear01	(4.83%)
5 Years	rr_AverageAnnualReturnYear05	5.58%
10 Years	rr_AverageAnnualReturnYear10	3.00%
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.55%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Interest Expense	rr_Component1OtherExpensesOverAssets	0.03%
Miscellaneous Other Expense	rr_Component2OtherExpensesOverAssets	0.12%
Other Expenses	rr_OtherExpensesOverAssets	0.15%
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.71%	[3]
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.05%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.66%	[2],[3]
1 Year	rr_ExpenseExampleYear01	67
3 Years	rr_ExpenseExampleYear03	222
5 Years	rr_ExpenseExampleYear05	390
10 Years	rr_ExpenseExampleYear10	$ 878
2004	rr_AnnualReturn2004	3.04%
2005	rr_AnnualReturn2005	1.23%
2006	rr_AnnualReturn2006	4.04%
2007	rr_AnnualReturn2007	3.25%
2008	rr_AnnualReturn2008	(4.00%)
2009	rr_AnnualReturn2009	13.38%
2010	rr_AnnualReturn2010	3.82%
2011	rr_AnnualReturn2011	11.32%
2012	rr_AnnualReturn2012	8.43%
2013	rr_AnnualReturn2013	(2.85%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	7.08%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2010
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(4.09%)
1 Year	rr_AverageAnnualReturnYear01	(2.85%)
5 Years	rr_AverageAnnualReturnYear05	6.66%
10 Years	rr_AverageAnnualReturnYear10	4.03%
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | Return After Taxes on Distributions | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.07%)
5 Years	rr_AverageAnnualReturnYear05	6.60%
10 Years	rr_AverageAnnualReturnYear10	3.96%
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | Return After Taxes on Distributions and Sale of Fund Shares | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(0.23%)
5 Years	rr_AverageAnnualReturnYear05	6.05%
10 Years	rr_AverageAnnualReturnYear10	3.95%
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | S&P Municipal Bond Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.55%)
5 Years	rr_AverageAnnualReturnYear05	6.34%
10 Years	rr_AverageAnnualReturnYear10	4.33%
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | S&P Intermediate Municipal Bond Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(0.98%)	[5]
5 Years	rr_AverageAnnualReturnYear05	5.64%	[5]
10 Years	rr_AverageAnnualReturnYear10	4.49%	[5]
Investor A, C and Institutional | BlackRock Strategic Municipal Opportunities Fund of BlackRock Municipal Series Trust | S&P Municipal Bond Investment Grade Index (65%); S&P Municipal Bond High Yield Index (30%); Barclays Taxable Municipal: U.S. Aggregate Eligible Index (5%) (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.09%)	[5]
5 Years	rr_AverageAnnualReturnYear05	8.13%	[5]
10 Years	rr_AverageAnnualReturnYear10	4.74%	[5]

[1] A contingent deferred sales charge ("CDSC") of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

[2] As described in the "Management of the Fund" section of the Fund's prospectus on page 31, BlackRock Advisors, LLC has contractually agreed to waive 0.05% of its management fee until October 1, 2015. The agreement may be terminated upon 90 days' notice by a majority of the non-interested trustees of the Fund or by a vote of a majority of the outstanding voting securities of the Fund.

[3] The Total Annual Fund Operating Expenses and the Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements do not correlate to the ratio of expenses to average net assets given in the Fund's most recent annual report, which does not include Acquired Fund Fees and Expenses.

[4] There is no CDSC on Investor C Shares after one year.

[5] Effective January 27, 2014, the Fund replaced the S&P Intermediate Municipal Bond Index, a benchmark against which it measured performance, with a customized weighted index comprised of the returns of the S&P Municipal Bond Investment Grade Index (65%), the S&P Municipal Bond High Yield Index (30%), and the Barclays Taxable Municipal: U.S. Aggregate Eligible Index (5%). Fund management believes the customized weighted index more accurately reflects the investment strategies of the Fund.