| 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 $30 0.59% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 98.6% Exchange-Traded Funds 1.0% Other Assets and Liabilities 0.4% |
| 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 $20 0.39% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 98.6% Exchange-Traded Funds 1.0% Other Assets and Liabilities 0.4% |
| 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 $19 0.36% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 98.6% Exchange-Traded Funds 1.0% Other Assets and Liabilities 0.4% |
| 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 $43 0.84% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 98.6% Exchange-Traded Funds 1.0% Other Assets and Liabilities 0.4% |
| 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 $82 1.59% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 98.6% Exchange-Traded Funds 1.0% Other Assets and Liabilities 0.4% |
| 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 $23 0.46% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 99.1% Exchange-Traded Funds 0.5% Other Assets and Liabilities 0.4% |
| 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 $13 0.26% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 99.1% Exchange-Traded Funds 0.5% Other Assets and Liabilities 0.4% |
| 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 $12 0.23% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 99.1% Exchange-Traded Funds 0.5% Other Assets and Liabilities 0.4% |
| 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 $36 0.71% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 99.1% Exchange-Traded Funds 0.5% Other Assets and Liabilities 0.4% |
| 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 $74 1.46% |
| 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% |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 99.1% Exchange-Traded Funds 0.5% Other Assets and Liabilities 0.4% |
| 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 $25 0.49% |
| 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 Holdings 86 7-Day Current Yield - Investor Class 2.66 % 7-Day Effective Yield - Investor Class 2.69 % |
| Holdings [Text Block] | Fund Holdings Types of Investments in Portfolio (as a % of net assets) Municipal Securities 99.5% Other Assets and Liabilities 0.5% |
| 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. |
