Document Type Document Type Performance Table Footnotes Performance Table Footnotes Expense Example, with Redemption, 5 Years Expense Example, with Redemption, 5 Years Other Expenses (as a percentage of Assets): Other Expenses (as a percentage of Assets): Risk Caption Risk Caption Expense Example, with Redemption, 3 Years Expense Example, with Redemption, 3 Years Thirty Day Tax Equivalent Yield Thirty Day Tax Equivalent Yield Expense Example, with Redemption, 1 Year Expense Example, with Redemption, 1 Year Expense Example Closing [Text Block] Expense Example Closing [Text Block] Expense Footnotes [Text Block] Expense Footnotes [Text Block] Component3 Other Expenses Component3 Other Expenses C CLASS HIGH-YIELD MUNICIPAL FUND, C CLASS HIGH-YIELD MUNICIPAL FUND, C CLASS, C000017688, AYMCX Performance Availability Phone [Text] Performance Availability Phone [Text] Tax-Free Money Market Fund Tax-Free Money Market Fund Tax-Free Money Market Fund, S000006473 Bar Chart [Heading] Bar Chart [Heading] Performance Additional Market Index [Text] Performance Additional Market Index [Text] Risk Lose Money [Text] Risk Lose Money [Text] Expense Example, No Redemption Narrative [Text Block] Expense Example, No Redemption Narrative [Text Block] Expense [Heading] Expense [Heading] Expenses Restated to Reflect Current [Text] Expenses Restated to Reflect Current [Text] Money Market Seven Day Yield Phone Money Market Seven Day Yield Phone Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage of Offering Price) Registrant Name Registrant Name Index No Deduction for Fees, Expenses, Taxes [Text] Index No Deduction for Fees, Expenses, Taxes [Text] Other Expenses, New Fund, Based on Estimates [Text] Other Expenses, New Fund, Based on Estimates [Text] Performance Measure [Axis] Performance Measure [Axis] Distribution or Similar (Non 12b-1) Fees Distribution or Similar (Non 12b-1) Fees Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Strategy Narrative [Text Block] Strategy Narrative [Text Block] Redemption Fee Redemption Fee Portfolio Turnover [Heading] Portfolio Turnover [Heading] Bar Chart Closing [Text Block] Bar Chart Closing [Text Block] Thirty Day Yield Thirty Day Yield MANAGED ACCOUNT SHARES SERIES N MANAGED ACCOUNT SHARES SERIES N MANAGED ACCOUNT SHARES SERIES N, S000068227 Shareholder Fees Caption [Text] Shareholder Fees Caption [Text] Bar Chart and Performance Table [Heading] Bar Chart and Performance Table [Heading] Money Market Seven Day Yield Money Market Seven Day Yield Performance Information Illustrates Variability of Returns [Text] Performance Information Illustrates Variability of Returns [Text] Performance Table Does Reflect Sales Loads Performance Table Does Reflect Sales Loads Lowest Quarterly Return, Date Lowest Quarterly Return, Date Objective, Secondary [Text Block] Objective, Secondary [Text Block] Highest Quarterly Return, Label Highest Quarterly Return, Label INVESTOR CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, INVESTOR CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, INVESTOR CLASS, C000017689, TWTIX Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text] Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text] Expense Example, with Redemption, 10 Years Expense Example, with Redemption, 10 Years Legal Entity Identifier Legal Entity Identifier I CLASS HIGH-YIELD MUNICIPAL FUND, INSTITUTIONAL CLASS HIGH-YIELD MUNICIPAL FUND, INSTITUTIONAL CLASS, C000088012, AYMIX LONG-TERM TAX-FREE FUND LONG-TERM TAX-FREE FUND LONG-TERM TAX-FREE FUND, S000006474 After Taxes on Distributions and Sales After Taxes on Distributions and Sales Prospectus: Prospectus: Maximum Cumulative Sales Charge (as a percentage of Offering Price) Maximum Cumulative Sales Charge (as a percentage of Offering Price) Expense Breakpoint Discounts [Text] Expense Breakpoint Discounts [Text] Bar Chart [Table] Bar Chart [Table] Shareholder Fee, Other Shareholder Fee, Other Amendment Description Amendment Description Acquired Fund Fees and Expenses Acquired Fund Fees and Expenses Expenses Range of Exchange Fees [Text Block] Expenses Range of Exchange Fees [Text Block] Thirty Day Yield Column [Text] Thirty Day Yield Column [Text] Risk/Return: Risk/Return: Operating Expenses Caption [Text] Operating Expenses Caption [Text] Fee Waiver or Reimbursement Fee Waiver or Reimbursement Performance Table Closing [Text Block] Performance Table Closing [Text Block] Bar Chart, Returns for Class Not Offered in Prospectus [Text] Bar Chart, Returns for Class Not Offered in Prospectus [Text] Maximum Account Fee (as a percentage of Assets) Maximum Account Fee (as a percentage of Assets) Y CLASS High-Yield Municipal Fund, Y Class High-Yield Municipal Fund, Y Class, C000189766 Expense Example by, Year, Caption [Text] Expense Example by, Year, Caption [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expense Example Narrative [Text Block] Expense Example Narrative [Text Block] Lowest Quarterly Return, Label Lowest Quarterly Return, Label Expense Breakpoint, Minimum Investment Required [Amount] Expense Breakpoint, Minimum Investment Required [Amount] Thirty Day Yield Caption Thirty Day Yield Caption Highest Quarterly Return Highest Quarterly Return Share Classes Share Classes Amendment Flag Amendment Flag Maximum Cumulative Sales Charge (as a percentage) Maximum Cumulative Sales Charge (as a percentage) Expenses Explanation of Nonrecurring Account Fee [Text] Expenses Explanation of Nonrecurring Account Fee [Text] MANAGED ACCOUNT SHARES SERIES CA MANAGED ACCOUNT SHARES SERIES CA MANAGED ACCOUNT SHARES SERIES CA, S000068226 Shareholder Fees Column [Text] Shareholder Fees Column [Text] Prospectus Prospectus Document [Axis] Document [Axis] After Taxes on Distributions After Taxes on Distributions Central Index Key Entity Central Index Key Component2 Other Expenses Component2 Other Expenses Annual Fund Operating Expenses [Table] Annual Fund Operating Expenses [Table] Objective [Heading] Objective [Heading] Caption Average Annual Return, Caption Expense Exchange Traded Fund Commissions [Text] Expense Exchange Traded Fund Commissions [Text] Management Fees (as a percentage of Assets) Management Fees (as a percentage of Assets) Expense Example, With Redemption [Table] Expense Example, With Redemption [Table] Document Effective Date Document Effective Date Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return, Date Expense Example by Year [Heading] Expense Example by Year [Heading] Since Inception Since Inception Fee Waiver or Reimbursement over Assets, Date of Termination Fee Waiver or Reimbursement over Assets, Date of Termination Risk Not Insured Depository Institution [Text] Risk Not Insured Depository Institution [Text] Thirty Day Yield Phone Thirty Day Yield Phone Performance Past Does Not Indicate Future [Text] Performance Past Does Not Indicate Future [Text] C CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, C CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, C CLASS, C000088014, TWTCX MANAGED ACCOUNT SHARES SERIES CA MANAGED ACCOUNT SHARES SERIES CA CLASS MANAGED ACCOUNT SHARES SERIES CA CLASS, C000218416, ACAMX Shareholder Fees [Table] Shareholder Fees [Table] Risk Footnotes [Text Block] Risk Footnotes [Text Block] Exchange Fee Exchange Fee Year to Date Return, Label Year to Date Return, Label Column Average Annual Return, Column Name Performance Table Heading Performance Table Heading Strategy Portfolio Concentration [Text] Strategy Portfolio Concentration [Text] INVESTOR CLASS TAX-FREE MONEY MARKET FUND, INVESTOR CLASS TAX-FREE MONEY MARKET FUND, INVESTOR CLASS, C000017692, BNTXX Risk Closing [Text Block] Risk Closing [Text Block] Net Expenses (as a percentage of Assets) Net Expenses (as a percentage of Assets) Y CLASS Intermediate-Term Tax-Free Bond Fund, Y Class Intermediate-Term Tax-Free Bond Fund, Y Class, C000189767 Distribution and Service (12b-1) Fees Distribution and Service (12b-1) Fees Performance Table One Class of after Tax Shown [Text] Performance Table One Class of after Tax Shown [Text] Annual Return 2005 Annual Return 2005 Annual Return 2004 Annual Return 2004 Money Market Seven Day Yield, Caption [Text] Money Market Seven Day Yield, Caption [Text] Annual Return 2003 Annual Return 2003 Annual Return 2002 Annual Return 2002 Share Class [Axis] Share Class [Axis] Annual Return 2001 Annual Return 2001 Annual Return, Column [Text] Annual Return, Column [Text] Annual Return 2000 Annual Return 2000 A CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, A CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, A CLASS, C000088013, TWWOX Annual Return 2009 Annual Return 2009 Expense Example, No Redemption, 10 Years Expense Example, No Redemption, 10 Years Annual Return 2008 Annual Return 2008 Annual Return 2007 Annual Return 2007 Performance Table Not Relevant to Tax Deferred Performance Table Not Relevant to Tax Deferred Annual Return 2006 Annual Return 2006 Bar Chart Footnotes [Text Block] Bar Chart Footnotes [Text Block] Objective, Primary [Text Block] Objective, Primary [Text Block] Portfolio Turnover, Rate Portfolio Turnover, Rate Performance Table Market Index Changed Performance Table Market Index Changed Expense Example [Heading] Expense Example [Heading] Barclays Municipal Bond Index Barclays Municipal Bond Index Barclays Municipal Bond Index Label Label Annual Return 2016 Annual Return 2016 Money Market Seven Day Tax Equivalent Yield Money Market Seven Day Tax Equivalent Yield Annual Return 2015 Annual Return 2015 Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] Annual Return 2014 Annual Return 2014 Annual Return 2013 Annual Return 2013 Annual Return 2012 Annual Return 2012 Annual Return 2011 Annual Return 2011 Annual Return 2010 Annual Return 2010 Strategy [Heading] Strategy [Heading] T CLASS Intermediate-Term Tax-Free Bond Fund, T Class Intermediate-Term Tax-Free Bond Fund, T Class, C000189768 Annual Return 2019 Annual Return 2019 Risk Nondiversified Status [Text] Risk Nondiversified Status [Text] Annual Return 2018 Annual Return 2018 Exchange Fee (as a percentage of Amount Redeemed) Exchange Fee (as a percentage of Amount Redeemed) Annual Return 2017 Annual Return 2017 Performance One Year or Less [Text] Performance One Year or Less [Text] Expense Example, No Redemption, 3 Years Expense Example, No Redemption, 3 Years Portfolio Turnover [Text Block] Portfolio Turnover [Text Block] Expense Example, No Redemption, 1 Year Expense Example, No Redemption, 1 Year Maximum Deferred Sales Charge (as a percentage) Maximum Deferred Sales Charge (as a percentage) Expense Example, No Redemption, 5 Years Expense Example, No Redemption, 5 Years INTERMEDIATE-TERM TAX-FREE BOND FUND INTERMEDIATE-TERM TAX-FREE BOND FUND INTERMEDIATE-TERM TAX-FREE BOND FUND, S000006472 Performance Narrative [Text Block] Performance Narrative [Text Block] Risk Narrative [Text Block] Risk Narrative [Text Block] I CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, INSTITUTIONAL CLASS INTERMEDIATE-TERM TAX-FREE BOND FUND, INSTITUTIONAL CLASS, C000017691, AXBIX 10 Years 10 Years Inception Date Inception Date Annual Return 2020 Annual Return 2020 Risk [Text] Risk [Text] Risk/Return [Heading] Risk/Return [Heading] Annual Return, Inception Date Annual Return, Inception Date Bar Chart, Year to Date Return Bar Chart, Year to Date Return Acquired Fund Fees and Expenses, Based on Estimates [Text] Acquired Fund Fees and Expenses, Based on Estimates [Text] Expense Example, No Redemption, By Year, Caption [Text] Expense Example, No Redemption, By Year, Caption [Text] Expenses Deferred Charges [Text Block] Expenses Deferred Charges [Text Block] Market Index Performance [Table] Market Index Performance [Table] Expense Narrative [Text Block] Expense Narrative [Text Block] Prospectus Date Prospectus Date 1 Year 1 Year Performance Table Narrative Performance Table Narrative Highest Quarterly Return, Date Highest Quarterly Return, Date 5 Years 5 Years Risk [Heading] Risk [Heading] A CLASS HIGH-YIELD MUNICIPAL FUND, A CLASS HIGH-YIELD MUNICIPAL FUND, A CLASS, C000017686, AYMAX S&P Intermediate Term National AMT-Free Municipal Bond Index S&P Intermediate Term National AMT-Free Municipal Bond Index S&P Intermediate Term National AMT-Free Municipal Bond Index Expense Example Footnotes [Text Block] Expense Example Footnotes [Text Block] Series [Axis] Series [Axis] Annual Return 1993 Annual Return 1993 Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Annual Return 1994 Annual Return 1994 Annual Return 1991 Annual Return 1991 Annual Return 1992 Annual Return 1992 Performance Availability Website Address [Text] Performance Availability Website Address [Text] Document Period End Date Document Period End Date Annual Return 1990 Annual Return 1990 Annual Return Caption [Text] Annual Return Caption [Text] Bar Chart Narrative [Text Block] Bar Chart Narrative [Text Block] Before Taxes Before Taxes Maximum Account Fee Maximum Account Fee Expense Example, No Redemption [Table] Expense Example, No Redemption [Table] S&P Municipal Bond 50% Investment Grade/50% High Yield Index S&P Municipal Bond California 50% Investment Grade/50% High Yield Index S&P Municipal Bond California 50% Investment Grade/50% High Yield Index Entity Inv Company Type Entity Inv Company Type Annual Return 1999 Annual Return 1999 Annual Return 1997 Annual Return 1997 Annual Return 1998 Annual Return 1998 Lowest Quarterly Return Lowest Quarterly Return Annual Return 1995 Annual Return 1995 Annual Return 1996 Annual Return 1996 Performance [Table] Performance [Table] Money Market Seven Day Yield Column [Text] Money Market Seven Day Yield Column [Text] Performance Table Explanation after Tax Higher Performance Table Explanation after Tax Higher Component1 Other Expenses Component1 Other Expenses Trading Symbol Trading Symbol HIGH-YIELD MUNICIPAL FUND HIGH-YIELD MUNICIPAL FUND HIGH-YIELD MUNICIPAL FUND, S000006471 Risk Column [Text] Risk Column [Text] Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee (as a percentage of Amount Redeemed) MANAGED ACCOUNT SHARES SERIES N MANAGED ACCOUNT SHARES SERIES N Class MANAGED ACCOUNT SHARES SERIES N Class, C000218417 Series Series INVESTOR CLASS HIGH-YIELD MUNICIPAL FUND, INVESTOR CLASS HIGH-YIELD MUNICIPAL FUND, INVESTOR CLASS, C000017685, ABHYX Expenses (as a percentage of Assets) Expenses (as a percentage of Assets) Performance Table Uses Highest Federal Rate Performance Table Uses Highest Federal Rate Bar Chart Does Not Reflect Sales Loads [Text] Bar Chart Does Not Reflect Sales Loads [Text] AMERICAN CENTURY MUNICIPAL TRUST AMERICAN CENTURY MUNICIPAL TRUST AMERICAN CENTURY MUNICIPAL TRUST Operating Expenses Column [Text] Operating Expenses Column [Text] Document Creation Date Document Creation Date Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Expenses Represent Both Master and Feeder [Text] Expenses Represent Both Master and Feeder [Text]