v3.26.1
Shareholder Report
 12 Months Ended
Feb. 28, 2026
USD ($)
$ / shares
Shareholder Report [Line Items]  
Document Type N-CSR
Amendment Flag false
Registrant Name Franklin Municipal Securities Trust
Entity Central Index Key 0000881309
Entity Investment Company Type N-1A
Document Period End Date Feb. 28, 2026
Shareholder Report Annual or Semi-Annual annual shareholder report
Class A  
Shareholder Report [Line Items]  
Fund Name Franklin California High Yield Municipal Fund
Class Name Class A
Trading Symbol FCQAX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (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 A
$83
0.81%
Expenses Paid, Amount $ 83
Expense Ratio, Percent 0.81%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended February 28, 2026, Class A shares of Franklin California High Yield Municipal Fund returned 3.74%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
↑
Selection in bonds with no external credit rating
↑
Underweight to bonds with 30 years to maturity
↑
Selection in B rated bonds
Top detractors from performance:
↓
Overweight to bonds with no external credit rating
↓
Overweight to bonds with 20 years to maturity
↓
Underweight bonds with 5 years or less to maturity  
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026
 
1 Year
5 Year
10 Year
Class A
3.74
1.03
2.60
Class A (with sales charge)
-0.15
0.26
2.20
Bloomberg Municipal Bond Index
4.96
1.44
2.43
Bloomberg Municipal Bond California Exempt Index
4.98
1.45
2.37
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 3,281,260,262
Holdings Count | $ / shares 745
Advisory Fees Paid, Amount $ 13,902,397
Investment Company Portfolio Turnover 13.89%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of February 28, 2026)
Total Net Assets
$3,281,260,262
Total Number of Portfolio Holdings
745
Total Management Fee Paid
$13,902,397
Portfolio Turnover Rate
13.89%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of February 28, 2026)
Portfolio Composition* (% of Total Investments)
image
 [1]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class A1  
Shareholder Report [Line Items]  
Fund Name Franklin California High Yield Municipal Fund
Class Name Class A1
Trading Symbol FCAMX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (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 A1
$67
0.66%
Expenses Paid, Amount $ 67
Expense Ratio, Percent 0.66%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended February 28, 2026, Class A1 shares of Franklin California High Yield Municipal Fund returned 3.91%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
↑
Selection in bonds with no external credit rating
↑
Underweight to bonds with 30 years to maturity
↑
Selection in B rated bonds
Top detractors from performance:
↓
Overweight to bonds with no external credit rating
↓
Overweight to bonds with 20 years to maturity
↓
Underweight bonds with 5 years or less to maturity  
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026
 
1 Year
5 Year
10 Year
Class A1
3.91
1.18
2.70
Class A1 (with sales charge)
-0.04
0.41
2.31
Bloomberg Municipal Bond Index
4.96
1.44
2.43
Bloomberg Municipal Bond California Exempt Index
4.98
1.45
2.37
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 3,281,260,262
Holdings Count | $ / shares 745
Advisory Fees Paid, Amount $ 13,902,397
Investment Company Portfolio Turnover 13.89%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of February 28, 2026)
Total Net Assets
$3,281,260,262
Total Number of Portfolio Holdings
745
Total Management Fee Paid
$13,902,397
Portfolio Turnover Rate
13.89%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of February 28, 2026)
Portfolio Composition* (% of Total Investments)
image
 [2]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class C  
Shareholder Report [Line Items]  
Fund Name Franklin California High Yield Municipal Fund
Class Name Class C
Trading Symbol FCAHX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (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 C
$122
1.20%
Expenses Paid, Amount $ 122
Expense Ratio, Percent 1.20%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended February 28, 2026, Class C shares of Franklin California High Yield Municipal Fund returned 3.20%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
↑
Selection in bonds with no external credit rating
↑
Underweight to bonds with 30 years to maturity
↑
Selection in B rated bonds
Top detractors from performance:
↓
Overweight to bonds with no external credit rating
↓
Overweight to bonds with 20 years to maturity
↓
Underweight bonds with 5 years or less to maturity  
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026
 
1 Year
5 Year
10 Year
Class C
3.20
0.58
2.11
Class C (with sales charge)
2.21
0.58
2.11
Bloomberg Municipal Bond Index
4.96
1.44
2.43
Bloomberg Municipal Bond California Exempt Index
4.98
1.45
2.37
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 3,281,260,262
Holdings Count | $ / shares 745
Advisory Fees Paid, Amount $ 13,902,397
Investment Company Portfolio Turnover 13.89%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of February 28, 2026)
Total Net Assets
$3,281,260,262
Total Number of Portfolio Holdings
745
Total Management Fee Paid
$13,902,397
Portfolio Turnover Rate
13.89%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of February 28, 2026)
Portfolio Composition* (% of Total Investments)
image
 [3]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class R6  
Shareholder Report [Line Items]  
Fund Name Franklin California High Yield Municipal Fund
Class Name Class R6
Trading Symbol FCAQX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (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 R6
$52
0.51%
Expenses Paid, Amount $ 52
Expense Ratio, Percent 0.51%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended February 28, 2026, Class R6 shares of Franklin California High Yield Municipal Fund returned 4.05%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
↑
Selection in bonds with no external credit rating
↑
Underweight to bonds with 30 years to maturity
↑
Selection in B rated bonds
Top detractors from performance:
↓
Overweight to bonds with no external credit rating
↓
Overweight to bonds with 20 years to maturity
↓
Underweight bonds with 5 years or less to maturity  
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026
 
1 Year
5 Year
10 Year
Class R6
4.05
1.30
2.83
Bloomberg Municipal Bond Index
4.96
1.44
2.43
Bloomberg Municipal Bond California Exempt Index
4.98
1.45
2.37
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 3,281,260,262
Holdings Count | $ / shares 745
Advisory Fees Paid, Amount $ 13,902,397
Investment Company Portfolio Turnover 13.89%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of February 28, 2026)
Total Net Assets
$3,281,260,262
Total Number of Portfolio Holdings
745
Total Management Fee Paid
$13,902,397
Portfolio Turnover Rate
13.89%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of February 28, 2026)
Portfolio Composition* (% of Total Investments)
image
 [4]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Advisor Class  
Shareholder Report [Line Items]  
Fund Name Franklin California High Yield Municipal Fund
Class Name Advisor Class
Trading Symbol FVCAX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin California High Yield Municipal Fund for the period March 1, 2025, to February 28, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (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
Advisor Class
$57
0.56%
Expenses Paid, Amount $ 57
Expense Ratio, Percent 0.56%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended February 28, 2026, Advisor Class shares of Franklin California High Yield Municipal Fund returned 4.00%. The Fund compares its performance to the Bloomberg Municipal Bond California Exempt Index, which returned 4.98% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
↑
Selection in bonds with no external credit rating
↑
Underweight to bonds with 30 years to maturity
↑
Selection in B rated bonds
Top detractors from performance:
↓
Overweight to bonds with no external credit rating
↓
Overweight to bonds with 20 years to maturity
↓
Underweight bonds with 5 years or less to maturity  
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended February 28, 2026
 
1 Year
5 Year
10 Year
Advisor Class
4.00
1.28
2.79
Bloomberg Municipal Bond Index
4.96
1.44
2.43
Bloomberg Municipal Bond California Exempt Index
4.98
1.45
2.37
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 3,281,260,262
Holdings Count | $ / shares 745
Advisory Fees Paid, Amount $ 13,902,397
Investment Company Portfolio Turnover 13.89%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of February 28, 2026)
Total Net Assets
$3,281,260,262
Total Number of Portfolio Holdings
745
Total Management Fee Paid
$13,902,397
Portfolio Turnover Rate
13.89%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of February 28, 2026)
Portfolio Composition* (% of Total Investments)
image
 [5]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
[1]
* Does not include derivatives, except purchased options, if any.  
[2]
* Does not include derivatives, except purchased options, if any.  
[3]
* Does not include derivatives, except purchased options, if any.  
[4]
* Does not include derivatives, except purchased options, if any.  
[5]
* Does not include derivatives, except purchased options, if any.