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Shareholder Report
 6 Months Ended
Nov. 30, 2024
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name BlackRock Municipal Series Trust
Entity Central Index Key 0000799113
Entity Investment Company Type N-1A
Document Period End Date Nov. 30, 2024
C000011342 [Member]  
Shareholder Report [Line Items]  
Fund Name BlackRock Strategic Municipal Opportunities Fund
Class Name Institutional Shares
Trading Symbol MAMTX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Strategic Municipal Opportunities Fund (the “Fund”) for the period of June 1, 2024 to November 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.
Additional Information Phone Number (800) 441‑7762
Additional Information Website blackrock.com/fundreports
Expenses [Text Block]
What were the Fund costs for the last six months ?
(based on a hypothetical $10,000 investment)
Class name Costs of a $10,000
investment		 Costs paid as a percentage of a
$10,000 investment
Institutional Shares $36 0.71%(a)
​(a)
Annualized.
Expenses Paid, Amount $ 36
Expense Ratio, Percent 0.71% [1]
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Average Annual Return [Table Text Block]
Average annual total returns
6-Month
Total
Returns		 1 Year 5 Years 10 Years
Institutional Shares 4.76 % 7.12 % 0.89 % 2.50 %
Bloomberg Municipal Bond Index 4.54 4.93 1.35 2.45
Customized Reference Benchmark 4.94 6.41 1.67 N/A
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information.
Net Assets $ 3,952,789,242
Holdings Count | Holding 618
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
Key Fund statistics
Net Assets $3,952,789,242
Number of Portfolio Holdings 618
Portfolio Turnover Rate 20%
Holdings [Text Block]
What did the Fund invest in?
(as of November 30, 2024)
Sector allocation
Sector(a) Percent of Total
Investments(b)
Utilities 23.2 %
County/City/Special District/School District 19.8 %
Transportation 14.8 %
State 11.6 %
Corporate 11.1 %
Health 6.2 %
Education 4.9 %
Housing 4.3 %
Tobacco 2.8 %
Commercial Services & Supplies 0.7 %
Other* 0.6 %
Credit quality allocation
Credit Rating(c) Percent of Total
Investments(b)
AAA/Aaa 14.2 %
AA/Aa 41.7 %
A 15.5 %
BBB/Baa 4.0 %
BB/Ba 2.7 %
B 0.4 %
N/R(d) 21.5 %
​(a)
For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
​(b)
Excludes short-term securities.
​(c)
For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
​(d)
The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
​*
Ten largest sectors are presented. Additional sectors are found in Other.
Credit Quality Explanation [Text Block] The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
Credit Ratings Selection [Text Block] For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
C000038983 [Member]  
Shareholder Report [Line Items]  
Fund Name BlackRock Strategic Municipal Opportunities Fund
Class Name Investor A Shares
Trading Symbol MEMTX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Strategic Municipal Opportunities Fund (the “Fund”) for the period of June 1, 2024 to November 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.
Additional Information Phone Number (800) 441‑7762
Additional Information Website blackrock.com/fundreports
Expenses [Text Block]
What were the Fund costs for the last six months ?
(based on a hypothetical $10,000 investment)
Class name Costs of a $10,000
investment		 Costs paid as a percentage of a
$10,000 investment
Investor A Shares $46 0.90%(a)
​(a)
Annualized.
Expenses Paid, Amount $ 46
Expense Ratio, Percent 0.90% [2]
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Average Annual Return [Table Text Block]
Average annual total returns
6-Month
Total
Returns		 1 Year 5 Years 10 Years
Investor A Shares 4.66 % 6.91 % 0.66 % 2.28 %
Investor A Shares (with sales charge) 0.21 2.37 (0.21 ) 1.84
Bloomberg Municipal Bond Index 4.54 4.93 1.35 2.45
Customized Reference Benchmark 4.94 6.41 1.67 N/A
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information.
Net Assets $ 3,952,789,242
Holdings Count | Holding 618
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
Key Fund statistics
Net Assets $3,952,789,242
Number of Portfolio Holdings 618
Portfolio Turnover Rate 20%
Holdings [Text Block]
What did the Fund invest in?
(as of November 30, 2024)
Sector allocation
Sector(a) Percent of Total
Investments(b)
Utilities 23.2 %
County/City/Special District/School District 19.8 %
Transportation 14.8 %
State 11.6 %
Corporate 11.1 %
Health 6.2 %
Education 4.9 %
Housing 4.3 %
Tobacco 2.8 %
Commercial Services & Supplies 0.7 %
Other* 0.6 %
Credit quality allocation
Credit Rating(c) Percent of Total
Investments(b)
AAA/Aaa 14.2 %
AA/Aa 41.7 %
A 15.5 %
BBB/Baa 4.0 %
BB/Ba 2.7 %
B 0.4 %
N/R(d) 21.5 %
​(a)
For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
​(b)
Excludes short-term securities.
​(c)
For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
​(d)
The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
​*
Ten largest sectors are presented. Additional sectors are found in Other.
Credit Quality Explanation [Text Block] The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
Credit Ratings Selection [Text Block] For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
C000011339 [Member]  
Shareholder Report [Line Items]  
Fund Name BlackRock Strategic Municipal Opportunities Fund
Class Name Investor A1 Shares
Trading Symbol MDMTX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Strategic Municipal Opportunities Fund (the “Fund”) for the period of June 1, 2024 to November 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.
Additional Information Phone Number (800) 441‑7762
Additional Information Website blackrock.com/fundreports
Expenses [Text Block]
What were the Fund costs for the last six months ?
(based on a hypothetical $10,000 investment)
Class name Costs of a $10,000
investment		 Costs paid as a percentage of a
$10,000 investment
Investor A1 Shares $40 0.77%(a)
​(a)
Annualized.
Expenses Paid, Amount $ 40
Expense Ratio, Percent 0.77% [3]
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Average Annual Return [Table Text Block]
Average annual total returns
6-Month
Total
Returns		 1 Year 5 Years 10 Years
Investor A1 Shares 4.73 % 7.05 % 0.82 % 2.43 %
Bloomberg Municipal Bond Index 4.54 4.93 1.35 2.45
Customized Reference Benchmark 4.94 6.41 1.67 N/A
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information.
Net Assets $ 3,952,789,242
Holdings Count | Holding 618
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
Key Fund statistics
Net Assets $3,952,789,242
Number of Portfolio Holdings 618
Portfolio Turnover Rate 20%
Holdings [Text Block]
What did the Fund invest in?
(as of November 30, 2024)
Sector allocation
Sector(a) Percent of Total
Investments(b)
Utilities 23.2 %
County/City/Special District/School District 19.8 %
Transportation 14.8 %
State 11.6 %
Corporate 11.1 %
Health 6.2 %
Education 4.9 %
Housing 4.3 %
Tobacco 2.8 %
Commercial Services & Supplies 0.7 %
Other* 0.6 %
Credit quality allocation
Credit Rating(c) Percent of Total
Investments(b)
AAA/Aaa 14.2 %
AA/Aa 41.7 %
A 15.5 %
BBB/Baa 4.0 %
BB/Ba 2.7 %
B 0.4 %
N/R(d) 21.5 %
​(a)
For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
​(b)
Excludes short-term securities.
​(c)
For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
​(d)
The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
​*
Ten largest sectors are presented. Additional sectors are found in Other.
Credit Quality Explanation [Text Block] The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
Credit Ratings Selection [Text Block] For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
C000038984 [Member]  
Shareholder Report [Line Items]  
Fund Name BlackRock Strategic Municipal Opportunities Fund
Class Name Investor C Shares
Trading Symbol MFMTX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Strategic Municipal Opportunities Fund (the “Fund”) for the period of June 1, 2024 to November 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.
Additional Information Phone Number (800) 441‑7762
Additional Information Website blackrock.com/fundreports
Expenses [Text Block]
What were the Fund costs for the last six months ?
(based on a hypothetical $10,000 investment)
Class name Costs of a $10,000
investment		 Costs paid as a percentage of a
$10,000 investment
Investor C Shares $86 1.68%(a)
​(a)
Annualized.
Expenses Paid, Amount $ 86
Expense Ratio, Percent 1.68% [4]
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Average Annual Return [Table Text Block]
Average annual total returns
6-Month
Total
Returns		 1 Year 5 Years 10 Years
Investor C Shares 4.25 % 6.08 % (0.10 )% 1.66 %
Investor C Shares (with sales charge) 3.25 5.08 (0.10 ) 1.66
Bloomberg Municipal Bond Index 4.54 4.93 1.35 2.45
Customized Reference Benchmark 4.94 6.41 1.67 N/A
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information.
Net Assets $ 3,952,789,242
Holdings Count | Holding 618
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
Key Fund statistics
Net Assets $3,952,789,242
Number of Portfolio Holdings 618
Portfolio Turnover Rate 20%
Holdings [Text Block]
What did the Fund invest in?
(as of November 30, 2024)
Sector allocation
Sector(a) Percent of Total
Investments(b)
Utilities 23.2 %
County/City/Special District/School District 19.8 %
Transportation 14.8 %
State 11.6 %
Corporate 11.1 %
Health 6.2 %
Education 4.9 %
Housing 4.3 %
Tobacco 2.8 %
Commercial Services & Supplies 0.7 %
Other* 0.6 %
Credit quality allocation
Credit Rating(c) Percent of Total
Investments(b)
AAA/Aaa 14.2 %
AA/Aa 41.7 %
A 15.5 %
BBB/Baa 4.0 %
BB/Ba 2.7 %
B 0.4 %
N/R(d) 21.5 %
​(a)
For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
​(b)
Excludes short-term securities.
​(c)
For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
​(d)
The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
​*
Ten largest sectors are presented. Additional sectors are found in Other.
Credit Quality Explanation [Text Block] The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
Credit Ratings Selection [Text Block] For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
C000199785 [Member]  
Shareholder Report [Line Items]  
Fund Name BlackRock Strategic Municipal Opportunities Fund
Class Name Class K Shares
Trading Symbol MKMTX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Strategic Municipal Opportunities Fund (the “Fund”) for the period of June 1, 2024 to November 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441‑7762.
Additional Information Phone Number (800) 441‑7762
Additional Information Website blackrock.com/fundreports
Expenses [Text Block]
What were the Fund costs for the last six months ?
(based on a hypothetical $10,000 investment)
Class name Costs of a $10,000
investment		 Costs paid as a percentage of a
$10,000 investment
Class K Shares $32 0.62%(a)
​(a)
Annualized.
Expenses Paid, Amount $ 32
Expense Ratio, Percent 0.62% [5]
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Average Annual Return [Table Text Block]
Average annual total returns
6-Month
Total
Returns		 1 Year 5 Years 10 Years
Class K Shares 4.81 % 7.21 % 0.97 % 2.55 %
Bloomberg Municipal Bond Index 4.54 4.93 1.35 2.45
Customized Reference Benchmark 4.94 6.41 1.67 N/A
Performance Inception Date Jan. 25, 2018
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information.
Net Assets $ 3,952,789,242
Holdings Count | Holding 618
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
Key Fund statistics
Net Assets $3,952,789,242
Number of Portfolio Holdings 618
Portfolio Turnover Rate 20%
Holdings [Text Block]
What did the Fund invest in?
(as of November 30, 2024)
Sector allocation
Sector(a) Percent of Total
Investments(b)
Utilities 23.2 %
County/City/Special District/School District 19.8 %
Transportation 14.8 %
State 11.6 %
Corporate 11.1 %
Health 6.2 %
Education 4.9 %
Housing 4.3 %
Tobacco 2.8 %
Commercial Services & Supplies 0.7 %
Other* 0.6 %
Credit quality allocation
Credit Rating(c) Percent of Total
Investments(b)
AAA/Aaa 14.2 %
AA/Aa 41.7 %
A 15.5 %
BBB/Baa 4.0 %
BB/Ba 2.7 %
B 0.4 %
N/R(d) 21.5 %
​(a)
For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.
​(b)
Excludes short-term securities.
​(c)
For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
​(d)
The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
​*
Ten largest sectors are presented. Additional sectors are found in Other.
Credit Quality Explanation [Text Block] The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors and individual investments. Using this approach, the investment adviser has deemed certain of these unrated securities as investment grade quality. As of November 30, 2024, the market value of unrated securities deemed by the investment adviser to be investment grade represents less than 1.0% of total investments.
Credit Ratings Selection [Text Block] For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
[1] Annualized.
[2] Annualized.
[3] Annualized.
[4] Annualized.
[5] Annualized.