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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 AMERICAN CENTURY MUNICIPAL TRUST
Entity Central Index Key 0000746458
Entity Investment Company Type N-1A
Document Period End Date Nov. 30, 2024
C000017685 [Member]  
Shareholder Report [Line Items]  
Fund Name High-Yield Municipal Fund
Class Name Investor Class
Trading Symbol ABHYX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about High-Yield Municipal 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Material Fund Change Notice [Text Block] This report describes changes to the fund that occurred during the reporting period.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Investor Class$300.59%
Expenses Paid, Amount $ 30
Expense Ratio, Percent 0.59%
Net Assets $ 611,550,447
Holdings Count | holding 383
Advisory Fees Paid, Amount $ 1,433,090
Investment Company, Portfolio Turnover 18.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities98.6%
Exchange-Traded Funds1.0%
Other Assets and Liabilities0.4%
 
 
Material Fund Change [Text Block]
Fund Changes
Beginning October 2024, the total eligible investments required to qualify for a waiver of the annual account maintenance fee changed from $10,000 to $25,000. Such fee will also be waived for any accounts for which the shareholder has elected to receive electronic delivery of all fund/account documents.
Material Fund Change Expenses [Text Block] Beginning October 2024, the total eligible investments required to qualify for a waiver of the annual account maintenance fee changed from $10,000 to $25,000. Such fee will also be waived for any accounts for which the shareholder has elected to receive electronic delivery of all fund/account documents.
C000088012 [Member]  
Shareholder Report [Line Items]  
Fund Name High-Yield Municipal Fund
Class Name I Class
Trading Symbol AYMIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about High-Yield Municipal 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
I Class$200.39%
Expenses Paid, Amount $ 20
Expense Ratio, Percent 0.39%
Net Assets $ 611,550,447
Holdings Count | holding 383
Advisory Fees Paid, Amount $ 1,433,090
Investment Company, Portfolio Turnover 18.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities98.6%
Exchange-Traded Funds1.0%
Other Assets and Liabilities0.4%
 
 
C000189766 [Member]  
Shareholder Report [Line Items]  
Fund Name High-Yield Municipal Fund
Class Name Y Class
Trading Symbol AYMYX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about High-Yield Municipal 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Y Class$190.36%
Expenses Paid, Amount $ 19
Expense Ratio, Percent 0.36%
Net Assets $ 611,550,447
Holdings Count | holding 383
Advisory Fees Paid, Amount $ 1,433,090
Investment Company, Portfolio Turnover 18.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities98.6%
Exchange-Traded Funds1.0%
Other Assets and Liabilities0.4%
 
 
C000017686 [Member]  
Shareholder Report [Line Items]  
Fund Name High-Yield Municipal Fund
Class Name A Class
Trading Symbol AYMAX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about High-Yield Municipal 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
A Class$430.84%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.84%
Net Assets $ 611,550,447
Holdings Count | holding 383
Advisory Fees Paid, Amount $ 1,433,090
Investment Company, Portfolio Turnover 18.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities98.6%
Exchange-Traded Funds1.0%
Other Assets and Liabilities0.4%
 
 
C000017688 [Member]  
Shareholder Report [Line Items]  
Fund Name High-Yield Municipal Fund
Class Name C Class
Trading Symbol AYMCX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about High-Yield Municipal 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
C Class$821.59%
Expenses Paid, Amount $ 82
Expense Ratio, Percent 1.59%
Net Assets $ 611,550,447
Holdings Count | holding 383
Advisory Fees Paid, Amount $ 1,433,090
Investment Company, Portfolio Turnover 18.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities98.6%
Exchange-Traded Funds1.0%
Other Assets and Liabilities0.4%
 
 
C000017689 [Member]  
Shareholder Report [Line Items]  
Fund Name Intermediate-Term Tax-Free Bond Fund
Class Name Investor Class
Trading Symbol TWTIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Intermediate-Term Tax-Free Bond 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Material Fund Change Notice [Text Block] This report describes changes to the fund that occurred during the reporting period.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Investor Class$230.46%
Expenses Paid, Amount $ 23
Expense Ratio, Percent 0.46%
Net Assets $ 3,705,717,425
Holdings Count | holding 1,541
Advisory Fees Paid, Amount $ 5,082,433
Investment Company, Portfolio Turnover 21.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities99.1%
Exchange-Traded Funds0.5%
Other Assets and Liabilities0.4%
 
 
Material Fund Change [Text Block]
Fund Changes
Beginning October 2024, the total eligible investments required to qualify for a waiver of the annual account maintenance fee changed from $10,000 to $25,000. Such fee will also be waived for any accounts for which the shareholder has elected to receive electronic delivery of all fund/account documents.
Material Fund Change Expenses [Text Block] Beginning October 2024, the total eligible investments required to qualify for a waiver of the annual account maintenance fee changed from $10,000 to $25,000. Such fee will also be waived for any accounts for which the shareholder has elected to receive electronic delivery of all fund/account documents.
C000017691 [Member]  
Shareholder Report [Line Items]  
Fund Name Intermediate-Term Tax-Free Bond Fund
Class Name I Class
Trading Symbol AXBIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Intermediate-Term Tax-Free Bond 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
I Class$130.26%
Expenses Paid, Amount $ 13
Expense Ratio, Percent 0.26%
Net Assets $ 3,705,717,425
Holdings Count | holding 1,541
Advisory Fees Paid, Amount $ 5,082,433
Investment Company, Portfolio Turnover 21.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities99.1%
Exchange-Traded Funds0.5%
Other Assets and Liabilities0.4%
 
 
C000189767 [Member]  
Shareholder Report [Line Items]  
Fund Name Intermediate-Term Tax-Free Bond Fund
Class Name Y Class
Trading Symbol ATBYX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Intermediate-Term Tax-Free Bond 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Y Class$120.23%
Expenses Paid, Amount $ 12
Expense Ratio, Percent 0.23%
Net Assets $ 3,705,717,425
Holdings Count | holding 1,541
Advisory Fees Paid, Amount $ 5,082,433
Investment Company, Portfolio Turnover 21.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities99.1%
Exchange-Traded Funds0.5%
Other Assets and Liabilities0.4%
 
 
C000088013 [Member]  
Shareholder Report [Line Items]  
Fund Name Intermediate-Term Tax-Free Bond Fund
Class Name A Class
Trading Symbol TWWOX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Intermediate-Term Tax-Free Bond 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
A Class$360.71%
Expenses Paid, Amount $ 36
Expense Ratio, Percent 0.71%
Net Assets $ 3,705,717,425
Holdings Count | holding 1,541
Advisory Fees Paid, Amount $ 5,082,433
Investment Company, Portfolio Turnover 21.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities99.1%
Exchange-Traded Funds0.5%
Other Assets and Liabilities0.4%
 
 
C000088014 [Member]  
Shareholder Report [Line Items]  
Fund Name Intermediate-Term Tax-Free Bond Fund
Class Name C Class
Trading Symbol TWTCX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Intermediate-Term Tax-Free Bond 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
C Class$741.46%
Expenses Paid, Amount $ 74
Expense Ratio, Percent 1.46%
Net Assets $ 3,705,717,425
Holdings Count | holding 1,541
Advisory Fees Paid, Amount $ 5,082,433
Investment Company, Portfolio Turnover 21.00%
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities99.1%
Exchange-Traded Funds0.5%
Other Assets and Liabilities0.4%
 
 
C000017692 [Member]  
Shareholder Report [Line Items]  
Fund Name Tax-Free Money Market Fund
Class Name Investor Class
Trading Symbol BNTXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Tax-Free Money Market 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 americancentury.com/docs. You can also request this information by contacting us at 1-800-345-2021.
Material Fund Change Notice [Text Block] This report describes changes to the fund that occurred during the reporting period.
Additional Information Phone Number 1-800-345-2021
Additional Information Website americancentury.com/docs
Expenses [Text Block]
What were the fund costs for the last six months? (based on a hypothetical $10,000 investment)
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Investor Class$250.49%
Expenses Paid, Amount $ 25
Expense Ratio, Percent 0.49%
Net Assets $ 150,049,094
Holdings Count | holding 86
Advisory Fees Paid, Amount $ 386,376
Additional Fund Statistics [Text Block]
Fund Statistics
Net Assets$150,049,094
Management Fees (dollars paid during the reporting period)$386,376
Total Number of Portfolio Holdings86
7-Day Current Yield - Investor Class2.66 %
7-Day Effective Yield - Investor Class2.69 %
Holdings [Text Block]
Fund Holdings
Types of Investments in Portfolio (as a % of net assets)
Municipal Securities99.5%
Other Assets and Liabilities0.5%
 
 
 
Material Fund Change [Text Block]
Fund Changes
Beginning October 2024, the total eligible investments required to qualify for a waiver of the annual account maintenance fee changed from $10,000 to $25,000. Such fee will also be waived for any accounts for which the shareholder has elected to receive electronic delivery of all fund/account documents.
Material Fund Change Expenses [Text Block] Beginning October 2024, the total eligible investments required to qualify for a waiver of the annual account maintenance fee changed from $10,000 to $25,000. Such fee will also be waived for any accounts for which the shareholder has elected to receive electronic delivery of all fund/account documents.