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Label Element Value
Prospectus: rr_ProspectusTable  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Oct. 31, 2016
Entity Registrant Name dei_EntityRegistrantName AMERICAN CENTURY MUTUAL FUNDS, INC.
Central Index Key dei_EntityCentralIndexKey 0000100334
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Apr. 07, 2017
Document Effective Date dei_DocumentEffectiveDate Apr. 10, 2017
Prospectus Date rr_ProspectusDate Apr. 10, 2017
American Century Mutual Funds, Inc | BALANCED FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Balanced Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective 
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth and current income by investing approximately 60% of its assets in equity securities and the remainder in bonds and other fixed-income securities. 
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover 
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 104% of the average value of its portfolio. 
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 104.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
For the equity portion of Balanced, the portfolio managers select stocks using quantitative management techniques in a two-step process. First, the managers rank stocks, primarily those of large (those with a market cap greater than $2 billion), publicly-traded U.S. companies from most attractive to least attractive based on an objective set of measures, including valuation, quality, growth and sentiment. Second, the portfolio managers use a quantitative model to build a portfolio of stocks from the ranking described above that they believe will provide the optimal balance between risk and expected return. The portfolio managers generally sell a stock when they believe it has become less attractive relative to other opportunities, its risk characteristics outweigh its return opportunity or specific events alter its prospects.
For the fixed-income portion of the fund, the portfolio managers invest in a diversified portfolio of high- and medium-grade non-money market debt securities. These securities, which may be payable in U.S. or foreign currencies, may include corporate bonds and notes, government securities and securities backed by mortgages or other assets. Shorter-term debt securities round out the portfolio. 
Risk [Heading] rr_RiskHeading Principal Risks 
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
•
Style Risk — If at any time the market is not favoring the quantitative investment style used to manage the fund’s equity portion, that portion’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Investment Process Risk — Stocks selected by the portfolio managers using quantitative models may perform differently than expected due to the portfolio managers’ judgments regarding the factors used in the models, the weight placed on each factor, changes from the factors’ historical trends, and technical issues with the construction and implementation of the models (including, for example, data problems and/or software or other implementation issues). There is no guarantee that the use of the quantitative models will result in effective investment decisions for the fund. Additionally, the commonality of portfolio holdings across quantitative investment managers may amplify losses.
•
Benchmark Correlation — The performance of the fund’s equity portion will be similar to the performance of the S&P 500 Index. If the S&P 500 goes down, it is likely that the fund’s performance will go down.
•
Market Risk — The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Interest Rate Risk — Investments in debt securities are sensitive to interest rate changes. Generally, the value of debt securities and the funds that hold them decline as interest rates rise. The fund’s fixed-income investments are designed to reduce this risk. Interest rate risk, however, is generally higher for the fixed-income portion of Balanced than for funds that have shorter-weighted maturities, such as money market funds and short-term bond funds. A period of rising interest rates may negatively affect the fund’s performance.
•
Credit Risk — Debt securities, even investment-grade debt securities, are subject to credit risk. Credit risk is the risk that the inability or perceived inability of the issuer to make interest and principal payments will cause the value of the securities to decrease. As a result the fund’s share price could also decrease. Changes in the credit rating of a debt security held by the fund could have a similar effect.
•
Prepayment Risk — The fund may invest in debt securities backed by mortgages or other assets. If these underlying assets are prepaid, the fund may benefit less from declining interest rates than funds of similar maturity that invest less heavily in mortgage- and asset-backed securities.
•
Foreign Securities Risk — Foreign securities have certain unique risks, such as currency risk, social, political and economic risk, and foreign market and trading risk. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
Derivative Risk — The use of derivative instruments involves risks different from, or possibly greater than, the risks associated with investing directly in securities and other traditional instruments. Derivatives are subject to a number of risks, including liquidity, interest rate, market, credit and correlation risk.
•
Liquidity Risk — The fund may also be subject to liquidity risk. During periods of market turbulence or unusually low trading activity, in order to meet redemptions it may be necessary for the fund to sell securities at prices that could have an adverse effect on the fund’s share price. Changing regulatory and market conditions, including increases in interest rates and credit spreads may adversely affect the liquidity of the fund’s investments.
•
Price Volatility — The value of the fund’s shares may fluctuate significantly in the short term.
•
Principal Loss — At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. 
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss — At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. 
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance 
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.
The blended index is considered the benchmark for Balanced. It combines two widely known indices in proportion to the asset mix of the fund. Accordingly, 60% of the index is represented by the S&P 500 Index, which reflects the approximately 60% of the fund’s assets invested in stocks. The blended index’s remaining 40% is represented by the Bloomberg Barclays U.S. Aggregate Bond Index, which reflects the roughly 40% of the fund’s assets invested in fixed-income securities. 
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown. 
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The blended index is considered the benchmark for Balanced. It combines two widely known indices in proportion to the asset mix of the fund. Accordingly, 60% of the index is represented by the S&P 500 Index, which reflects the approximately 60% of the fund’s assets invested in stocks. The blended index’s remaining 40% is represented by the Bloomberg Barclays U.S. Aggregate Bond Index, which reflects the roughly 40% of the fund’s assets invested in fixed-income securities. 
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns 
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown. 
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (3Q 2009): 10.38% Lowest Performance Quarter (4Q 2008): -12.18%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
American Century Mutual Funds, Inc | BALANCED FUND | Barclays US Aggregate Bond Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Bloomberg Barclays U.S. Aggregate Bond Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 2.65%
5 Years rr_AverageAnnualReturnYear05 2.23%
10 Years rr_AverageAnnualReturnYear10 4.34%
American Century Mutual Funds, Inc | BALANCED FUND | Blended Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Blended Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 8.31%
5 Years rr_AverageAnnualReturnYear05 9.69%
10 Years rr_AverageAnnualReturnYear10 6.21%
American Century Mutual Funds, Inc | BALANCED FUND | S&P 500 Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel S&P 500® Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 11.96%
5 Years rr_AverageAnnualReturnYear05 14.64%
10 Years rr_AverageAnnualReturnYear10 6.94%
American Century Mutual Funds, Inc | BALANCED FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWBIX
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.90%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.91%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 93
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 291
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 504
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,120
Annual Return 2007 rr_AnnualReturn2007 5.01%
Annual Return 2008 rr_AnnualReturn2008 (20.33%)
Annual Return 2009 rr_AnnualReturn2009 16.36%
Annual Return 2010 rr_AnnualReturn2010 11.57%
Annual Return 2011 rr_AnnualReturn2011 5.43%
Annual Return 2012 rr_AnnualReturn2012 11.59%
Annual Return 2013 rr_AnnualReturn2013 17.35%
Annual Return 2014 rr_AnnualReturn2014 9.75%
Annual Return 2015 rr_AnnualReturn2015 (2.65%)
Annual Return 2016 rr_AnnualReturn2016 6.90%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.38%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (12.18%)
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 6.90%
5 Years rr_AverageAnnualReturnYear05 8.37%
10 Years rr_AverageAnnualReturnYear10 5.52%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 20, 1988
American Century Mutual Funds, Inc | BALANCED FUND | INVESTOR CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 6.23%
5 Years rr_AverageAnnualReturnYear05 6.61%
10 Years rr_AverageAnnualReturnYear10 4.26%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 20, 1988
American Century Mutual Funds, Inc | BALANCED FUND | INVESTOR CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 4.33%
5 Years rr_AverageAnnualReturnYear05 6.26%
10 Years rr_AverageAnnualReturnYear10 4.14%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 20, 1988
American Century Mutual Funds, Inc | BALANCED FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ABINX
Maximum Account Fee rr_MaximumAccountFee none [1]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.71%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 73
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 227
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 396
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 883
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 7.18%
5 Years rr_AverageAnnualReturnYear05 8.61%
10 Years rr_AverageAnnualReturnYear10 5.74%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2000
American Century Mutual Funds, Inc | BALANCED FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ABGNX
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.71%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 73
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 227
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 396
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 883
Label rr_AverageAnnualReturnLabel R5 Class1 Return Before Taxes [2]
1 Year rr_AverageAnnualReturnYear01 7.18% [2]
5 Years rr_AverageAnnualReturnYear05 8.61% [2]
10 Years rr_AverageAnnualReturnYear10 5.74% [2]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [2]
American Century Mutual Funds, Inc | GROWTH FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 36% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 36.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The portfolio managers look for stocks of companies they believe will increase in value over time. In implementing this strategy, the portfolio managers make their investment decisions based primarily on their analysis of individual companies, rather than on broad economic forecasts. Management of the fund is based on the belief that, over the long term, stock price movements follow growth in earnings, revenues and/or cash flow.
The portfolio managers use a variety of analytical research tools and techniques to identify the stocks of larger-sized companies that meet their investment criteria. Under normal market conditions, the fund’s portfolio will primarily consist of securities of companies demonstrating business improvement. Analytical indicators helping to identify signs of business improvement could include accelerating earnings or revenue growth rates, increasing cash flows, or other indications of the relative strength of a company’s business. These techniques help the portfolio managers buy or hold the stocks of companies they believe have favorable growth prospects and sell the stocks of companies whose characteristics no longer meet their criteria.
Although the portfolio managers intend to invest the fund’s assets primarily in U.S. securities, the fund may invest in securities of foreign companies when these securities meet the portfolio managers’ standards of selection.  
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
•
Growth Stocks – Investments in growth stocks may be more volatile than other stocks and the overall stock market. These stocks are typically priced higher than other stocks because of their growth potential, which may or may not be realized.
•
Style Risk – If at any time the market is not favoring the fund’s growth investment style, the fund’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Market Risk – The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Price Volatility – The value of the fund’s shares may fluctuate significantly in the short term.
•
Foreign Securities – The fund may invest in foreign securities, which can be riskier than investing in U.S. securities. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
Redemption Risk  – The fund may need to sell securities at times it would not otherwise do so in order to meet shareholder redemption requests. Selling securities to meet such redemptions may cause the fund to experience a loss, increase the fund’s transaction costs or have tax consequences. To the extent that a large shareholder (including a fund of funds or 529 college savings plan) invests in the fund, the fund may experience relatively large redemptions as such shareholder reallocates its assets.  
•
Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.  
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (1Q 2012): 15.91% Lowest Performance Quarter (4Q 2008): -22.91%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
American Century Mutual Funds, Inc | GROWTH FUND | Russell 1000 Growth Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Russell 1000® Growth Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 7.08%
5 Years rr_AverageAnnualReturnYear05 14.48%
10 Years rr_AverageAnnualReturnYear10 8.33%
American Century Mutual Funds, Inc | GROWTH FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWCGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.97%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 100
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 313
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 542
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,201
Annual Return 2007 rr_AnnualReturn2007 18.98%
Annual Return 2008 rr_AnnualReturn2008 (37.84%)
Annual Return 2009 rr_AnnualReturn2009 35.48%
Annual Return 2010 rr_AnnualReturn2010 17.64%
Annual Return 2011 rr_AnnualReturn2011 (0.90%)
Annual Return 2012 rr_AnnualReturn2012 13.91%
Annual Return 2013 rr_AnnualReturn2013 29.37%
Annual Return 2014 rr_AnnualReturn2014 11.22%
Annual Return 2015 rr_AnnualReturn2015 4.56%
Annual Return 2016 rr_AnnualReturn2016 4.15%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.91%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (22.91%)
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.15%
5 Years rr_AverageAnnualReturnYear05 12.27%
10 Years rr_AverageAnnualReturnYear10 7.62%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 30, 1971
American Century Mutual Funds, Inc | GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 2.93%
5 Years rr_AverageAnnualReturnYear05 9.97%
10 Years rr_AverageAnnualReturnYear10 6.42%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 30, 1971
American Century Mutual Funds, Inc | GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 3.38%
5 Years rr_AverageAnnualReturnYear05 9.56%
10 Years rr_AverageAnnualReturnYear10 6.08%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 30, 1971
American Century Mutual Funds, Inc | GROWTH FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWGIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [3]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [3]
Maximum Account Fee rr_MaximumAccountFee none [3]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.77%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 250
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 434
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.33%
5 Years rr_AverageAnnualReturnYear05 12.49%
10 Years rr_AverageAnnualReturnYear10 7.83%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 16, 1997
American Century Mutual Funds, Inc | GROWTH FUND | Y CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AGYWX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.62%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.63%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 202
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 352
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 787
Label rr_AverageAnnualReturnLabel Y Class1 Return Before Taxes [4]
1 Year rr_AverageAnnualReturnYear01 4.49% [4]
Since Inception rr_AverageAnnualReturnSinceInception 9.84% [4]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [4]
American Century Mutual Funds, Inc | GROWTH FUND | A CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TCRAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [5]
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.97%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.23%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 693
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 943
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,212
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,978
Label rr_AverageAnnualReturnLabel A Class2 Return Before Taxes [6]
1 Year rr_AverageAnnualReturnYear01 (2.13%) [6]
5 Years rr_AverageAnnualReturnYear05 10.67% [6]
10 Years rr_AverageAnnualReturnYear10 6.71% [6]
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 04, 1997 [6]
American Century Mutual Funds, Inc | GROWTH FUND | C CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWRCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.97%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 201
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 622
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,068
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,303
Label rr_AverageAnnualReturnLabel C Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.06%
5 Years rr_AverageAnnualReturnYear05 11.15%
10 Years rr_AverageAnnualReturnYear10 6.55% [7]
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 01, 2010
American Century Mutual Funds, Inc | GROWTH FUND | R CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AGWRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.97%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.48%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 151
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 469
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 809
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,767
Label rr_AverageAnnualReturnLabel R Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.60%
5 Years rr_AverageAnnualReturnYear05 11.71%
10 Years rr_AverageAnnualReturnYear10 7.08%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 29, 2003
American Century Mutual Funds, Inc | GROWTH FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AGWUX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.77%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 250
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 434
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Label rr_AverageAnnualReturnLabel R5 Class4 Return Before Taxes [8]
1 Year rr_AverageAnnualReturnYear01 4.33% [8]
5 Years rr_AverageAnnualReturnYear05 12.49% [8]
10 Years rr_AverageAnnualReturnYear10 7.83% [8]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [8]
American Century Mutual Funds, Inc | GROWTH FUND | R6 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AGRDX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.62%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.63%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 202
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 352
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 787
Label rr_AverageAnnualReturnLabel R6 Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.49%
Since Inception rr_AverageAnnualReturnSinceInception 9.84%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 26, 2013
American Century Mutual Funds, Inc | HERITAGE FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Heritage Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 62% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 62.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The portfolio managers look for stocks of medium-sized and smaller companies they believe will increase in value over time, using an investment strategy developed by the fund’s investment advisor. In implementing this strategy, the portfolio managers make their investment decisions based primarily on their analysis of individual companies, rather than on broad economic forecasts. Management of the fund is based on the belief that, over the long term, stock price movements follow growth in earnings and revenues. The portfolio managers’ principal analytical technique involves the identification of companies with earnings and revenues that are not only growing, but growing at an accelerating pace. This includes companies whose growth rates, although still negative, are less negative than prior periods, and companies whose growth rates are expected to accelerate. In addition to accelerating growth, the fund also considers companies demonstrating price strength relative to their peers. This means that the portfolio managers favor companies whose securities are the strongest performers compared to the overall market. These techniques help the portfolio managers buy or hold the stocks of companies they believe have favorable growth prospects and sell the stocks of companies whose characteristics no longer meet their criteria.
The fund will usually purchase common stocks of companies that are medium-sized and smaller at the time of purchase, but it will purchase securities of larger-sized companies as well.
Also, although the portfolio managers intend to invest the fund’s assets primarily in U.S. securities, the fund may invest in securities of foreign companies when these securities meet the portfolio managers’ standards of selection.
The fund may engage in active and frequent trading of portfolio securities to achieve its principal investment strategies. This may cause higher transaction costs and may affect performance. It may also result in the realization and distribution of capital gains.
Risk [Heading] rr_RiskHeading Principal Risks 
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
Growth Stocks – Investments in growth stocks may be more volatile than other stocks and the overall stock market. These stocks are typically priced higher than other stocks because of their growth potential, which may or may not be realized.
•
Mid Cap Stocks – The fund invests in mid-sized and smaller companies, which may be more volatile and subject to greater risk than larger companies. Smaller companies may have limited financial resources, product lines and markets, and their securities may trade less frequently and in more limited volumes than the securities of larger companies, which could lead to higher transaction costs.
•
Style Risk – If at any time the market is not favoring the fund’s growth investment style, the fund’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Foreign Securities – The fund may invest in foreign securities, which can be riskier than investing in U.S. securities. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
Price Volatility – The value of the fund’s shares may fluctuate significantly in the short term.
•
Market Risk – The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Redemption Risk –The fund may need to sell securities at times it would not otherwise do so in order to meet shareholder redemption requests. Selling securities to meet such redemptions may cause the fund to experience a loss, increase the fund’s transaction costs or have tax consequences. To the extent that a large shareholder (including a fund of funds or 529 college savings plan) invests in the fund, the fund may experience relatively large redemptions as such shareholder reallocates its assets.         
•
Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.     
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns 
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (3Q 2010): 18.36% Lowest Performance Quarter (4Q 2008): -26.63%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
American Century Mutual Funds, Inc | HERITAGE FUND | Russell Midcap Growth Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Russell Midcap® Growth Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 7.33%
5 Years rr_AverageAnnualReturnYear05 13.49%
10 Years rr_AverageAnnualReturnYear10 7.83%
American Century Mutual Funds, Inc | HERITAGE FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWHIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.00%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.00%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 102
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 319
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 553
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,225
Annual Return 2007 rr_AnnualReturn2007 45.77%
Annual Return 2008 rr_AnnualReturn2008 (46.17%)
Annual Return 2009 rr_AnnualReturn2009 36.85%
Annual Return 2010 rr_AnnualReturn2010 31.37%
Annual Return 2011 rr_AnnualReturn2011 (6.53%)
Annual Return 2012 rr_AnnualReturn2012 16.04%
Annual Return 2013 rr_AnnualReturn2013 31.02%
Annual Return 2014 rr_AnnualReturn2014 8.16%
Annual Return 2015 rr_AnnualReturn2015 1.91%
Annual Return 2016 rr_AnnualReturn2016 3.21%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.36%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.63%)
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.21%
5 Years rr_AverageAnnualReturnYear05 11.57%
10 Years rr_AverageAnnualReturnYear10 8.59%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 10, 1987
American Century Mutual Funds, Inc | HERITAGE FUND | INVESTOR CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 1.27%
5 Years rr_AverageAnnualReturnYear05 9.01%
10 Years rr_AverageAnnualReturnYear10 7.23%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 10, 1987
American Century Mutual Funds, Inc | HERITAGE FUND | INVESTOR CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 3.46%
5 Years rr_AverageAnnualReturnYear05 9.09%
10 Years rr_AverageAnnualReturnYear10 6.96%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 10, 1987
American Century Mutual Funds, Inc | HERITAGE FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ATHIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [9]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [9]
Maximum Account Fee rr_MaximumAccountFee none [9]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.80%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 82
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 256
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 445
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 990
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.42%
5 Years rr_AverageAnnualReturnYear05 11.79%
10 Years rr_AverageAnnualReturnYear10 8.80%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 16, 1997
American Century Mutual Funds, Inc | HERITAGE FUND | Y CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ATHYX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.65%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 67
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 208
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 363
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 811
Label rr_AverageAnnualReturnLabel Y Class1 Return Before Taxes [10]
1 Year rr_AverageAnnualReturnYear01 3.54% [10]
Since Inception rr_AverageAnnualReturnSinceInception 7.18% [10]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [10]
American Century Mutual Funds, Inc | HERITAGE FUND | A CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ATHAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [11]
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.00%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.25%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 695
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 949
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,223
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,999
Label rr_AverageAnnualReturnLabel A Class2 Return Before Taxes [12]
1 Year rr_AverageAnnualReturnYear01 (2.92%) [12]
5 Years rr_AverageAnnualReturnYear05 9.99% [12]
10 Years rr_AverageAnnualReturnYear10 7.67% [12]
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 11, 1997 [12]
American Century Mutual Funds, Inc | HERITAGE FUND | C CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AHGCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.00%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.00%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 203
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 628
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,079
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,324
Label rr_AverageAnnualReturnLabel C Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 2.24%
5 Years rr_AverageAnnualReturnYear05 10.46%
10 Years rr_AverageAnnualReturnYear10 7.51%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 26, 2001
American Century Mutual Funds, Inc | HERITAGE FUND | R CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ATHWX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.00%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 153
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 475
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 819
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,789
Label rr_AverageAnnualReturnLabel R Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 2.74%
5 Years rr_AverageAnnualReturnYear05 11.02%
Since Inception rr_AverageAnnualReturnSinceInception 5.19%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 28, 2007
American Century Mutual Funds, Inc | HERITAGE FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ATHGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.80%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 82
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 256
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 445
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 990
Label rr_AverageAnnualReturnLabel R5 Class3 Return Before Taxes [13]
1 Year rr_AverageAnnualReturnYear01 3.42% [13]
5 Years rr_AverageAnnualReturnYear05 11.79% [13]
10 Years rr_AverageAnnualReturnYear10 8.80% [13]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [13]
American Century Mutual Funds, Inc | HERITAGE FUND | R6 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ATHDX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.65%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 67
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 208
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 363
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 811
Label rr_AverageAnnualReturnLabel R6 Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.54%
Since Inception rr_AverageAnnualReturnSinceInception 7.18%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 26, 2013
American Century Mutual Funds, Inc | SELECT FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Select Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 16% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 16.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The portfolio managers look for stocks of companies they believe will increase in value over time. The portfolio managers make their investment decisions based primarily on their analysis of individual companies, rather than on broad economic forecasts. Management of the fund is based on the belief that, over the long term, stock price movements follow growth in earnings, revenues and/or cash flow.
The portfolio managers use a variety of analytical research tools and techniques to identify the stocks of larger-sized companies that meet their investment criteria. Under normal market conditions, the portfolio managers seek securities of companies whose earnings or revenues are not only growing, but growing at an accelerated pace. This includes companies whose growth rates, although still negative, are less negative than prior periods, and companies whose growth rates are expected to accelerate. Among other variables, the portfolio managers will consider a company’s valuation and profitability. Other analytical techniques include evaluating stock price momentum, as well as identifying additional signs of business improvement, such as increasing cash flows, or other indications of the relative strength of a company’s business. In addition to accelerating growth and other signs of business improvement, the fund also considers companies demonstrating price strength relative to their peers. This means that the portfolio managers favor companies whose securities are the strongest performers compared to the overall market. These techniques help the portfolio managers buy or hold the stocks of companies they believe have favorable growth prospects and sell the stocks of companies whose characteristics no longer meet their criteria.
Although the portfolio managers intend to invest the fund’s assets primarily in U.S. securities, the fund may invest in securities of foreign companies when these securities meet the portfolio managers’ standards of selection.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
•
Growth Stocks – Investments in growth stocks may be more volatile than other stocks and the overall stock market. These stocks are typically priced higher than other stocks because of their growth potential, which may or may not be realized.
•
Style Risk – If at any time the market is not favoring the fund’s growth investment style, the fund’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Foreign Securities – The fund may invest in foreign securities, which can be riskier than investing in U.S. securities. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
Market Risk – The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Price Volatility – The value of the fund’s shares may fluctuate significantly in the short term.
•
Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.        
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (1Q 2012): 17.25% Lowest Performance Quarter (4Q 2008): -21.82%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs. 
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs. 
American Century Mutual Funds, Inc | SELECT FUND | Russell 1000 Growth Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Russell 1000® Growth Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 7.08%
5 Years rr_AverageAnnualReturnYear05 14.48%
10 Years rr_AverageAnnualReturnYear10 8.33%
American Century Mutual Funds, Inc | SELECT FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWCIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 316
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 548
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,213
Annual Return 2007 rr_AnnualReturn2007 21.67%
Annual Return 2008 rr_AnnualReturn2008 (39.67%)
Annual Return 2009 rr_AnnualReturn2009 34.79%
Annual Return 2010 rr_AnnualReturn2010 14.58%
Annual Return 2011 rr_AnnualReturn2011 1.42%
Annual Return 2012 rr_AnnualReturn2012 14.74%
Annual Return 2013 rr_AnnualReturn2013 30.21%
Annual Return 2014 rr_AnnualReturn2014 10.52%
Annual Return 2015 rr_AnnualReturn2015 7.69%
Annual Return 2016 rr_AnnualReturn2016 5.48%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.25%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.82%)
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 5.48%
5 Years rr_AverageAnnualReturnYear05 13.39%
10 Years rr_AverageAnnualReturnYear10 7.98%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 30, 1971
American Century Mutual Funds, Inc | SELECT FUND | INVESTOR CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 4.57%
5 Years rr_AverageAnnualReturnYear05 12.28%
10 Years rr_AverageAnnualReturnYear10 7.25%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 30, 1971
American Century Mutual Funds, Inc | SELECT FUND | INVESTOR CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 3.87%
5 Years rr_AverageAnnualReturnYear05 10.67%
10 Years rr_AverageAnnualReturnYear10 6.42%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 30, 1971
American Century Mutual Funds, Inc | SELECT FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWSIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [14]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [14]
Maximum Account Fee rr_MaximumAccountFee none [14]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.79%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.79%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 81
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 253
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 439
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 978
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 5.71%
5 Years rr_AverageAnnualReturnYear05 13.62%
10 Years rr_AverageAnnualReturnYear10 8.20%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 13, 1997
American Century Mutual Funds, Inc | SELECT FUND | Y CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ASLWX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.64%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 66
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 799
Label rr_AverageAnnualReturnLabel Y Class1 Return Before Taxes [15]
1 Year rr_AverageAnnualReturnYear01 5.87% [15]
Since Inception rr_AverageAnnualReturnSinceInception 11.68% [15]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [15]
American Century Mutual Funds, Inc | SELECT FUND | A CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWCAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [16]
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 694
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 946
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,218
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,988
Label rr_AverageAnnualReturnLabel A Class2 Return Before Taxes [17]
1 Year rr_AverageAnnualReturnYear01 (0.81%) [17]
5 Years rr_AverageAnnualReturnYear05 11.79% [17]
10 Years rr_AverageAnnualReturnYear10 7.08% [17]
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 08, 1997 [17]
American Century Mutual Funds, Inc | SELECT FUND | C CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ACSLX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 202
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 625
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,073
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,314
Label rr_AverageAnnualReturnLabel C Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.45%
5 Years rr_AverageAnnualReturnYear05 12.27%
10 Years rr_AverageAnnualReturnYear10 6.91%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 31, 2003
American Century Mutual Funds, Inc | SELECT FUND | R CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ASERX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 152
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 472
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 814
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,778
Label rr_AverageAnnualReturnLabel R Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.97%
5 Years rr_AverageAnnualReturnYear05 12.83%
10 Years rr_AverageAnnualReturnYear10 7.44%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 29, 2005
American Century Mutual Funds, Inc | SELECT FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ASLGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.79%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.79%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 81
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 253
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 439
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 978
Label rr_AverageAnnualReturnLabel R5 Class3 Return Before Taxes [18]
1 Year rr_AverageAnnualReturnYear01 5.71% [18]
5 Years rr_AverageAnnualReturnYear05 13.62% [18]
10 Years rr_AverageAnnualReturnYear10 8.20% [18]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [18]
American Century Mutual Funds, Inc | SELECT FUND | R6 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ASDEX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.64%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 66
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 799
Label rr_AverageAnnualReturnLabel R6 Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 5.87%
Since Inception rr_AverageAnnualReturnSinceInception 11.68%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 26, 2013
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Small Cap Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 130% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 130.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information. 
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal market conditions, the fund will invest at least 80% of its net assets in small cap companies. The portfolio managers consider small cap companies to include those with a market capitalization that does not exceed that of the largest company in the Russell 2000 Growth Index.      
The portfolio managers look for stocks of smaller-sized companies they believe will increase in value over time, using an investment strategy developed by the fund’s investment advisor. In implementing this strategy, the portfolio managers make their investment decisions based primarily on their analysis of individual companies, rather than on broad economic forecasts. Management of the fund is based on the belief that, over the long term, stock price movements follow growth in earnings and revenues. The portfolio managers’ principal analytical technique involves the identification of companies with earnings and revenues that are not only growing, but growing at an accelerating pace. This includes companies whose growth rates, although still negative, are less negative than prior periods, and companies whose growth rates are expected to accelerate. In addition to accelerating growth, the fund also may consider companies whose stocks demonstrate price strength relative to their peers. This means that the portfolio managers favor companies whose securities are the strongest performers compared to the overall market. These techniques help the portfolio managers buy or hold the stocks of companies they believe have favorable growth prospects and sell the stocks of companies whose characteristics no longer meet their criteria.
Although the portfolio managers intend to invest the fund’s assets primarily in U.S. securities, the fund may invest in securities of foreign companies when these securities meet the portfolio managers’ standards of selection.
The fund may engage in active and frequent trading of portfolio securities to achieve its principal investment strategies. This may cause higher transaction costs and may affect performance. It may also result in the realization and distribution of capital gains.
Risk [Heading] rr_RiskHeading Principal Risks 
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
•
Growth Stocks – Investments in growth stocks may be more volatile than other stocks and the overall stock market. These stocks are typically priced higher than other stocks because of their growth potential, which may or may not be realized.
•
Small Cap Stocks – The smaller companies in which the fund invests may be more volatile and subject to greater risk than larger companies. Smaller companies may have limited financial resources, product lines and markets, and their securities may trade less frequently and in more limited volumes than the securities of larger companies, which could lead to higher transaction costs.
•
Style Risk – If at any time the market is not favoring the fund’s growth investment style, the fund’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Foreign Securities – The fund may invest in foreign securities, which can be riskier than investing in U.S. securities. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
IPO Risk – The fund’s performance may be affected by investments in initial public offerings.
•
Market Risk – The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Price Volatility – The value of the fund’s shares may fluctuate significantly in the short term.
•
Redemption Risk – The fund may need to sell securities at times it would not otherwise do so in order to meet shareholder redemption requests. Selling securities to meet such redemptions may cause the fund to experience a loss, increase the fund's transaction costs or have tax consequences. To the extent that a large shareholder (including a fund of funds or 529 college savings plan) invests in the fund, the fund may experience relatively large redemptions as such shareholder reallocates its assets.
•
Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.     
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss – At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund. 
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.        
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown. 
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com.
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown. 
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (4Q 2010): 19.60% Lowest Performance Quarter (3Q 2011): -25.36%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | Russell 2000 Growth Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Russell 2000® Growth Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 11.32%
5 Years rr_AverageAnnualReturnYear05 13.72%
10 Years rr_AverageAnnualReturnYear10 7.75%
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANOIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.36%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.36%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 139
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 431
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 745
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,634
Annual Return 2007 rr_AnnualReturn2007 23.81%
Annual Return 2008 rr_AnnualReturn2008 (42.00%)
Annual Return 2009 rr_AnnualReturn2009 24.85%
Annual Return 2010 rr_AnnualReturn2010 30.09%
Annual Return 2011 rr_AnnualReturn2011 (5.18%)
Annual Return 2012 rr_AnnualReturn2012 14.59%
Annual Return 2013 rr_AnnualReturn2013 40.78%
Annual Return 2014 rr_AnnualReturn2014 5.45%
Annual Return 2015 rr_AnnualReturn2015 (3.97%)
Annual Return 2016 rr_AnnualReturn2016 10.76%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 19.60%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (25.36%)
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 10.76%
5 Years rr_AverageAnnualReturnYear05 12.58%
10 Years rr_AverageAnnualReturnYear10 7.18%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 01, 2001
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 10.76%
5 Years rr_AverageAnnualReturnYear05 12.57%
10 Years rr_AverageAnnualReturnYear10 7.16%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 01, 2001
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 6.09%
5 Years rr_AverageAnnualReturnYear05 10.07%
10 Years rr_AverageAnnualReturnYear10 5.83%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 01, 2001
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANONX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [19]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [19]
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%) [19]
Maximum Account Fee rr_MaximumAccountFee none [19]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.16%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.16%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 118
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 369
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 639
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,409
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 10.97%
5 Years rr_AverageAnnualReturnYear05 12.77%
Since Inception rr_AverageAnnualReturnSinceInception 6.11%
Inception Date rr_AverageAnnualReturnInceptionDate May 18, 2007
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | Y CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANOYX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.01%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.01%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 103
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 322
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 559
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,236
Label rr_AverageAnnualReturnLabel Y Class1 Return Before Taxes [20]
1 Year rr_AverageAnnualReturnYear01 11.16% [20]
Since Inception rr_AverageAnnualReturnSinceInception 7.53% [20]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [20]
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | A CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANOAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [21]
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.36%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.61%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 730
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 1,055
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,401
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,375
Label rr_AverageAnnualReturnLabel A Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.14%
5 Years rr_AverageAnnualReturnYear05 10.97%
10 Years rr_AverageAnnualReturnYear10 6.28%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 31, 2003
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | C CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANOCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.36%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.36%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 240
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 738
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,261
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,692
Label rr_AverageAnnualReturnLabel C Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 9.59%
5 Years rr_AverageAnnualReturnYear05 11.45%
10 Years rr_AverageAnnualReturnYear10 6.10%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 31, 2003
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | R CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANORX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.36%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.86%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 189
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 586
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,007
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,177
Label rr_AverageAnnualReturnLabel R Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 10.23%
5 Years rr_AverageAnnualReturnYear05 11.99%
Since Inception rr_AverageAnnualReturnSinceInception 4.62%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 28, 2007
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANOGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.16%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.16%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 118
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 369
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 639
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,409
Label rr_AverageAnnualReturnLabel R5 Class2 Return Before Taxes [22]
1 Year rr_AverageAnnualReturnYear01 10.97% [22]
5 Years rr_AverageAnnualReturnYear05 12.77% [22]
Since Inception rr_AverageAnnualReturnSinceInception 6.11% [22]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [22]
American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | R6 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol ANODX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.01%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.01%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 103
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 322
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 559
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,236
Label rr_AverageAnnualReturnLabel R6 Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 11.16%
Since Inception rr_AverageAnnualReturnSinceInception 7.53%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 26, 2013
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Sustainable Equity Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock
Income is a secondary objective.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 71% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 71.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The fund will generally invest in larger-sized companies using a quantitative model that combines fundamental measures of a stock’s value and growth potential. To measure value, the managers may use ratios of stock price-to-earnings and stock price-to-cash flow, among others. To measure growth, the managers may use the rate of growth of a company’s earnings and cash flow and changes in its earnings estimates, as well as other factors. The model also considers price momentum. The portfolio managers also take environmental, social and governance ("ESG") factors into account in making investment decisions.  The portfolio managers attempt to build a portfolio of stocks that provides better returns than, and a dividend yield comparable to, the S&P 500® Index, without taking on significant additional risk.
Under normal market conditions, the fund will invest at least 80% of its net assets in equity securities.
Although the portfolio managers intend to invest the fund’s assets primarily in U.S. securities, the fund may invest in securities of foreign companies when these securities meet the portfolio managers’ standards of selection.
When determining whether to sell a security, the portfolio managers consider among other things, a security’s price, whether a security’s risk parameters outweigh its return opportunities, general market conditions, whether the security meets their ESG criteria, and any other factor deemed relevant by the portfolio managers.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
•
Style Risk - If at any time the market is not favoring the fund’s investment process, the fund’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Benchmark Correlation - The fund’s performance will be similar to the performance of its benchmark, the S&P 500® Index. If the fund’s benchmark goes down, it is likely that the fund’s performance will go down.
•
ESG Criteria Risk - Because the fund's ESG criteria may exclude the securities of certain issuers for nonfinancial reasons, the fund may forego some market opportunities available to funds that do not use ESG criteria.
•
Foreign Securities - The fund may invest in foreign securities, which can be riskier than investing in U.S. securities. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
Market Risk - The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Principal Loss - At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss - At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for A Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for A Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (3Q 2009): 15.47% Lowest Performance Quarter (4Q 2008): -20.53%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns  For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for A Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for A Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | S&P 500 Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel S&P 500® Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 11.96%
5 Years rr_AverageAnnualReturnYear05 14.64%
10 Years rr_AverageAnnualReturnYear10 6.94%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFDIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.00%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 102
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 319
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 553
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,225
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 8.99%
5 Years rr_AverageAnnualReturnYear05 13.12%
10 Years rr_AverageAnnualReturnYear10 7.04%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFEIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [23]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [23]
Maximum Account Fee rr_MaximumAccountFee none [23]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.79%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.80%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 82
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 256
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 445
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 990
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 9.19%
5 Years rr_AverageAnnualReturnYear05 13.34%
10 Years rr_AverageAnnualReturnYear10 7.26%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | Y CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFYDX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.64%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 67
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 208
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 363
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 811
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | A CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFDAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [24]
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.25%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 695
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 949
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,223
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,999
Annual Return 2007 rr_AnnualReturn2007 13.73%
Annual Return 2008 rr_AnnualReturn2008 (35.57%)
Annual Return 2009 rr_AnnualReturn2009 21.85%
Annual Return 2010 rr_AnnualReturn2010 13.51%
Annual Return 2011 rr_AnnualReturn2011 3.93%
Annual Return 2012 rr_AnnualReturn2012 15.01%
Annual Return 2013 rr_AnnualReturn2013 31.26%
Annual Return 2014 rr_AnnualReturn2014 13.69%
Annual Return 2015 rr_AnnualReturn2015 (1.92%)
Annual Return 2016 rr_AnnualReturn2016 8.73%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.47%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.53%)
Label rr_AverageAnnualReturnLabel A Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 2.50%
5 Years rr_AverageAnnualReturnYear05 11.52%
10 Years rr_AverageAnnualReturnYear10 6.15%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | A CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 2.28%
5 Years rr_AverageAnnualReturnYear05 11.28%
10 Years rr_AverageAnnualReturnYear10 5.89%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | A CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 1.60%
5 Years rr_AverageAnnualReturnYear05 9.18%
10 Years rr_AverageAnnualReturnYear10 4.90%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | C CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFDCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.00%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 203
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 628
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,079
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,324
Label rr_AverageAnnualReturnLabel C Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 7.87%
5 Years rr_AverageAnnualReturnYear05 11.99%
10 Years rr_AverageAnnualReturnYear10 5.97%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | R CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFDRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.99%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 153
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 475
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 819
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,789
Label rr_AverageAnnualReturnLabel R Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 8.44%
5 Years rr_AverageAnnualReturnYear05 12.55%
10 Years rr_AverageAnnualReturnYear10 6.50%
American Century Mutual Funds, Inc | SUSTAINABLE EQUITY FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AFDGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.79%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.80%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 82
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 256
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 445
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 990
Label rr_AverageAnnualReturnLabel R5 Class1 Return Before Taxes [25]
1 Year rr_AverageAnnualReturnYear01 9.19% [25]
5 Years rr_AverageAnnualReturnYear05 13.34% [25]
10 Years rr_AverageAnnualReturnYear10 7.26% [25]
American Century Mutual Funds, Inc | ULTRA FUND  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading Ultra® Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The fund seeks long-term capital growth. 
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses you may pay if you buy and hold shares of the fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 18% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 18.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in American Century Investments funds. More information about these and other discounts is available from your financial professional and in Calculation of Sales Charges on page 13 of the fund’s prospectus, Appendix A of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
The example below is intended to help you compare the costs of investing in the fund with the costs of investing in other mutual funds.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods, that you earn a 5% return each year, and that the fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
The portfolio managers look for stocks of companies they believe will increase in value over time. The portfolio managers make their investment decisions based primarily on their analysis of individual companies, rather than on broad economic forecasts. Management of the fund is based on the belief that, over the long term, stock price movements follow growth in earnings, revenues and/or cash flow.
The portfolio managers use a variety of analytical research tools and techniques to identify the stocks of larger-sized companies that meet their investment criteria. Under normal market conditions, the portfolio managers seek securities of companies whose earnings or revenues are not only growing, but growing at an accelerated pace. This includes companies whose growth rates, although still negative, are less negative than prior periods, and companies whose growth rates are expected to accelerate. Among other variables, the portfolio managers will consider the fund’s growth and momentum profile relative to the benchmark. Other analytical techniques help identify additional signs of business improvement, such as increasing cash flows, or other indications of the relative strength of a company’s business. In addition to accelerating growth and other signs of business improvement, the fund also considers companies demonstrating price strength relative to their peers. This means that the portfolio managers favor companies whose securities are the strongest performers compared to the overall market. These techniques help the portfolio managers buy or hold the stocks of companies they believe have favorable growth prospects and sell the stocks of companies whose characteristics no longer meet their criteria.
Although the portfolio managers intend to invest the fund’s assets primarily in U.S. securities, the fund may invest in securities of foreign companies when these securities meet the portfolio managers’ standards of selection.
Risk [Heading] rr_RiskHeading Principal Risks 
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
•
Growth Stocks — Investments in growth stocks may be more volatile than other stocks and the overall stock market. These stocks are typically priced higher than other stocks because of their growth potential, which may or may not be realized.
•
Style Risk — If at any time the market is not favoring the fund’s growth investment style, the fund’s gains may not be as big as, or its losses may be bigger than, those of other equity funds using different investment styles.
•
Market Risk — The value of the fund’s shares will go up and down based on the performance of the companies whose securities it owns and other factors generally affecting the securities market.
•
Price Volatility — The value of the fund’s shares may fluctuate significantly in the short term.
•
Foreign Securities — The fund may invest in foreign securities, which can be riskier than investing in U.S. securities. Securities of foreign issuers may be less liquid, more volatile and harder to value than U.S. securities.
•
Principal Loss — At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. 
Risk Lose Money [Text] rr_RiskLoseMoney Principal Loss — At any given time your shares may be worth less than the price you paid for them. In other words, it is possible to lose money by investing in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit, and it is not insured or guaranteed by the Federal Deposit Insurance Corporation (FDIC) or any other government agency. 
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Fund Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance. The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future. For current performance information, please visit americancentury.com.
Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Class shares. The table shows how the fund’s average annual returns for the periods shown compared with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress americancentury.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The fund’s past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales charges and account fees, if applicable, are not reflected in the bar chart. If those charges were included, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest Performance Quarter (1Q 2012): 15.53% Lowest Performance Quarter (4Q 2008): -21.50%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns For the calendar year ended December 31, 2016
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
The after-tax returns are shown only for Investor Class shares. After-tax returns for other share classes will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as 401(k) plans or IRAs.
American Century Mutual Funds, Inc | ULTRA FUND | Russell 1000 Growth Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel Russell 1000® Growth Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 7.08%
5 Years rr_AverageAnnualReturnYear05 14.48%
10 Years rr_AverageAnnualReturnYear10 8.33%
American Century Mutual Funds, Inc | ULTRA FUND | S&P 500 Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes    (reflects no deduction for fees, expenses or taxes)
Label rr_AverageAnnualReturnLabel S&P 500® Index    (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 11.96%
5 Years rr_AverageAnnualReturnYear05 14.64%
10 Years rr_AverageAnnualReturnYear10 6.94%
American Century Mutual Funds, Inc | ULTRA FUND | INVESTOR CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWCUX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee $ 25
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 100
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 313
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 542
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,201
Annual Return 2007 rr_AnnualReturn2007 21.83%
Annual Return 2008 rr_AnnualReturn2008 (41.74%)
Annual Return 2009 rr_AnnualReturn2009 35.36%
Annual Return 2010 rr_AnnualReturn2010 16.56%
Annual Return 2011 rr_AnnualReturn2011 1.19%
Annual Return 2012 rr_AnnualReturn2012 14.18%
Annual Return 2013 rr_AnnualReturn2013 36.91%
Annual Return 2014 rr_AnnualReturn2014 9.91%
Annual Return 2015 rr_AnnualReturn2015 6.16%
Annual Return 2016 rr_AnnualReturn2016 4.38%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Performance Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2012
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.53%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Performance Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (21.50%)
Label rr_AverageAnnualReturnLabel Investor Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.38%
5 Years rr_AverageAnnualReturnYear05 13.73%
10 Years rr_AverageAnnualReturnYear10 7.99%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 02, 1981
American Century Mutual Funds, Inc | ULTRA FUND | INVESTOR CLASS | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 3.24%
5 Years rr_AverageAnnualReturnYear05 12.56%
10 Years rr_AverageAnnualReturnYear10 7.01%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 02, 1981
American Century Mutual Funds, Inc | ULTRA FUND | INVESTOR CLASS | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 3.44%
5 Years rr_AverageAnnualReturnYear05 10.95%
10 Years rr_AverageAnnualReturnYear10 6.47%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 02, 1981
American Century Mutual Funds, Inc | ULTRA FUND | I CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWUIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [26]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [26]
Maximum Account Fee rr_MaximumAccountFee none [26]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.78%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 250
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 434
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Label rr_AverageAnnualReturnLabel I Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.60%
5 Years rr_AverageAnnualReturnYear05 13.96%
10 Years rr_AverageAnnualReturnYear10 8.20%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 14, 1996
American Century Mutual Funds, Inc | ULTRA FUND | Y CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AULYX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.63%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.63%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 202
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 352
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 787
Label rr_AverageAnnualReturnLabel Y Class1 Return Before Taxes [27]
1 Year rr_AverageAnnualReturnYear01 4.72% [27]
Since Inception rr_AverageAnnualReturnSinceInception 10.93% [27]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [27]
American Century Mutual Funds, Inc | ULTRA FUND | A CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWUAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [28]
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.23%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 693
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 943
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,212
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,978
Label rr_AverageAnnualReturnLabel A Class2 Return Before Taxes [29]
1 Year rr_AverageAnnualReturnYear01 (1.86%) [29]
5 Years rr_AverageAnnualReturnYear05 12.11% [29]
10 Years rr_AverageAnnualReturnYear10 7.08% [29]
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 02, 1996 [29]
American Century Mutual Funds, Inc | ULTRA FUND | C CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol TWCCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 201
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 622
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,068
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,303
Label rr_AverageAnnualReturnLabel C Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.34%
5 Years rr_AverageAnnualReturnYear05 12.60%
10 Years rr_AverageAnnualReturnYear10 6.91%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 29, 2001
American Century Mutual Funds, Inc | ULTRA FUND | R CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AULRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.48%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 151
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 469
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 809
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,767
Label rr_AverageAnnualReturnLabel R Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 3.84%
5 Years rr_AverageAnnualReturnYear05 13.16%
10 Years rr_AverageAnnualReturnYear10 7.45%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 29, 2003
American Century Mutual Funds, Inc | ULTRA FUND | R5 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AULGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.78%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.78%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 80
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 250
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 434
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 966
Label rr_AverageAnnualReturnLabel R5 Class3 Return Before Taxes [30]
1 Year rr_AverageAnnualReturnYear01 4.60% [30]
5 Years rr_AverageAnnualReturnYear05 13.96% [30]
10 Years rr_AverageAnnualReturnYear10 8.20% [30]
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017 [30]
American Century Mutual Funds, Inc | ULTRA FUND | R6 CLASS  
Prospectus: rr_ProspectusTable  
Trading Symbol dei_TradingSymbol AULDX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Maximum Account Fee rr_MaximumAccountFee none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.63%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets none
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.63%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 202
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 352
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 787
Label rr_AverageAnnualReturnLabel R6 Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 4.72%
Since Inception rr_AverageAnnualReturnSinceInception 10.93%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 26, 2013
[1] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[2] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 Class.
[3] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[4] Historical performance for the Y Class prior to its inception is based on the performance of R6 Class shares, which have the same expenses as the Y Class shares.
[5] Purchases of $1 million or more may be subject to a contingent deferred sales charge of 1.00% if the shares are redeemed within one year of the date of the purchase.
[6] Prior to March 1, 2010, the A Class was referred to as the Advisor Class and did not have a front-end sales charge. Performance prior to that date has been restated to reflect this charge.
[7] Historical performance for C Class prior to its inception is based on the performance of Investor Class shares. C Class performance has been adjusted to reflect differences in sales charges, if applicable, and expenses between classes.
[8] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 Class shares.
[9] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[10] Historical performance for the Y Class prior to its inception is based on the performance of R6 Class shares, which have the same expenses as the Y Class shares.
[11] Purchases of $1 million or more may be subject to a contingent deferred sales charge of 1.00% if the shares are redeemed within one year of the date of the purchase.
[12] Prior to September 4, 2007, this class was referred to as the Advisor Class and did not have a front-end sales charge. Performance prior to that date has been restated to reflect this charge.
[13] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 Class.
[14] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[15] Historical performance for the Y Class prior to its inception is based on the performance of R6 Class shares, which have the same expenses as the Y Class shares.
[16] Purchases of $1 million or more may be subject to a contingent deferred sales charge of 1.00% if the shares are redeemed within one year of the date of the purchase.
[17] Prior to September 4, 2007, this class was referred to as the Advisor Class and did not have a front-end sales charge. Performance prior to that date has been restated to reflect this charge.
[18] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 Class shares.
[19] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[20] Historical performance for the Y Class prior to its inception is based on the performance of R6 Class shares, which have the same expenses as the Y Class shares.
[21] Purchases of $1 million or more may be subject to a contingent deferred sales charge of 1.00% if the shares are redeemed within one year of the date of the purchase.
[22] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 class.
[23] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[24] Purchases of $1 million or more may be subject to a contingent deferred sales charge of 1.00% if the shares are redeemed within one year of the date of the purchase.
[25] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 Class shares.
[26] Prior to April 10, 2017, this class was referred to as the Institutional Class.
[27] Historical performance for the Y Class prior to its inception is based on the performance of R6 Class shares, which have the same expenses as the Y Class shares.
[28] Purchases of $1 million or more may be subject to a contingent deferred sales charge of 1.00% if the shares are redeemed within one year of the date of the purchase.
[29] Prior to September 4, 2007, this class was referred to as the Advisor Class and did not have a front-end sales charge. Performance prior to that date has been restated to reflect this charge.
[30] Historical performance for the R5 Class prior to its inception is based on the performance of I Class shares, which have the same expenses as the R5 Class shares.