Risk/Return: Prospectus: Document Information, Document [Axis] Document [Domain] AMERICAN CENTURY MUNICIPAL TRUST AMERICAN CENTURY MUNICIPAL TRUST Series [Axis] Entity [Domain] MANAGED ACCOUNT SHARES SERIES CA MANAGED ACCOUNT SHARES SERIES CA series MANAGED ACCOUNT SHARES SERIES CA series, S000068226 MANAGED ACCOUNT SHARES SERIES N MANAGED ACCOUNT SHARES SERIES N series MANAGED ACCOUNT SHARES SERIES N, S000068227 Share Class [Axis] Share Classes MANAGED ACCOUNT SHARES SERIES CA MANAGED ACCOUNT SHARES SERIES CA class MANAGED ACCOUNT SHARES SERIES CA class, C000218416, ACAMX MANAGED ACCOUNT SHARES SERIES N MANAGED ACCOUNT SHARES SERIES N class MANAGED ACCOUNT SHARES SERIES N, C000218417 Performance Measure [Axis] Before Taxes After Taxes on Distributions After Taxes on Distributions and Sales Risk/Return [Heading] Objective [Heading] Objective, Primary [Text Block] Objective, Secondary [Text Block] Expense [Heading] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Shareholder Fees [Table] Operating Expenses Caption [Text] Annual Fund Operating Expenses [Table] Expense Footnotes [Text Block] Expenses Deferred Charges [Text Block] Expenses Range of Exchange Fees [Text Block] Expense Example [Heading] Expense Example by Year [Heading] Expense Example Narrative [Text Block] Expense Example by, Year, Caption [Text] Expense Example, With Redemption [Table] Expense Example, No Redemption Narrative [Text Block] Expense Example, No Redemption, By Year, Caption [Text] Expense Example, No Redemption [Table] Expense Example Footnotes [Text Block] Expense Example Closing [Text Block] Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Strategy [Heading] Strategy Narrative [Text Block] Risk [Heading] Risk Narrative [Text Block] Risk Footnotes [Text Block] Risk Closing [Text Block] Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Bar Chart Narrative [Text Block] Bar Chart [Heading] Bar Chart [Table] Bar Chart Footnotes [Text Block] Bar Chart Closing [Text Block] Performance Table Heading Performance Table Narrative Performance [Table] Market Index Performance [Table] Performance Table Footnotes Performance Table Closing [Text Block] Operating Expenses: Operating Expenses Column [Text] Management Fees (as a percentage of Assets) Distribution and Service (12b-1) Fees Distribution or Similar (Non 12b-1) Fees Component1 Other Expenses Component2 Other Expenses Component3 Other Expenses Other Expenses (as a percentage of Assets): Acquired Fund Fees and Expenses Expenses (as a percentage of Assets) Fee Waiver or Reimbursement Net Expenses (as a percentage of Assets) Risk/Return Detail [Table] Bar Chart Table: Annual Return Caption [Text] Annual Return, Column [Text] Annual Return, Inception Date Annual Return 1990 Annual Return 1991 Annual Return 1992 Annual Return 1993 Annual Return 1994 Annual Return 1995 Annual Return 1996 Annual Return 1997 Annual Return 1998 Annual Return 1999 Annual Return 2000 Annual Return 2001 Annual Return 2002 Annual Return 2003 Annual Return 2004 Annual Return 2005 Annual Return 2006 Annual Return 2007 Annual Return 2008 Annual Return 2009 Annual Return 2010 Annual Return 2011 Annual Return 2012 Annual Return 2013 Annual Return 2014 Annual Return 2015 Annual Return 2016 Annual Return 2017 Annual Return 2018 Annual Return 2019 Annual Return 2020 Expense Example, No Redemption: Expense Example, No Redemption, By Year, Column [Text] Expense Example, No Redemption, 1 Year Expense Example, No Redemption, 3 Years Expense Example, No Redemption, 5 Years Expense Example, No Redemption, 10 Years Shareholder Fees: Shareholder Fees Column [Text] Maximum Cumulative Sales Charge (as a percentage of Offering Price) Maximum Cumulative Sales Charge (as a percentage) Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage) Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee Exchange Fee (as a percentage of Amount Redeemed) Exchange Fee Maximum Account Fee (as a percentage of Assets) Maximum Account Fee Shareholder Fee, Other Document Type Document Period End Date Entity Registrant Name Central Index Key Amendment Flag Amendment Description Trading Symbol Document Creation Date Document Effective Date Prospectus Date Fee Waiver or Reimbursement over Assets, Date of Termination Portfolio Turnover, Rate Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expense Exchange Traded Fund Commissions [Text] Expenses Represent Both Master and Feeder [Text] Expenses Explanation of Nonrecurring Account Fee [Text] Other Expenses, New Fund, Based on Estimates [Text] Acquired Fund Fees and Expenses, Based on Estimates [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expenses Restated to Reflect Current [Text] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Expense Example, with Redemption, 1 Year Expense Example, with Redemption, 3 Years Expense Example, with Redemption, 5 Years Expense Example, with Redemption, 10 Years Strategy Portfolio Concentration [Text] Risk Lose Money [Text] Risk Nondiversified Status [Text] Risk Money Market Fund [Text] Risk Not Insured Depository Institution [Text] Risk Caption Risk Column [Text] Risk [Text] Performance Information Illustrates Variability of Returns [Text] Performance One Year or Less [Text] Performance Additional Market Index [Text] Performance Availability Phone [Text] Performance Availability Website Address [Text] Performance Past Does Not Indicate Future [Text] Bar Chart Does Not Reflect Sales Loads [Text] Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] Bar Chart, Returns for Class Not Offered in Prospectus [Text] Year to Date Return, Label Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return Highest Quarterly Return, Label Highest Quarterly Return, Date Highest Quarterly Return Lowest Quarterly Return, Label Lowest Quarterly Return, Date Lowest Quarterly Return Performance Table Does Reflect Sales Loads Performance Table Market Index Changed Index No Deduction for Fees, Expenses, Taxes [Text] Performance Table Uses Highest Federal Rate Performance Table Not Relevant to Tax Deferred Performance Table One Class of after Tax Shown [Text] Performance Table Explanation after Tax Higher Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text] Caption Column Label 1 Year 5 Years 10 Years Since Inception Inception Date Money Market Seven Day Yield, Caption [Text] Money Market Seven Day Yield Column [Text] Money Market Seven Day Yield Phone Money Market Seven Day Yield Money Market Seven Day Tax Equivalent Yield Thirty Day Yield Caption Thirty Day Yield Column [Text] Thirty Day Yield Phone Thirty Day Yield Thirty Day Tax Equivalent Yield Expense Example: Expense Example, By Year, Column [Text] Average Annual Return: