Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Document Type

dei_DocumentType

485BPOS

Document Period End Date

dei_DocumentPeriodEndDate

Oct. 31, 2014

Registrant Name

dei_EntityRegistrantName

AMERICAN CENTURY MUTUAL FUNDS, INC.

Central Index Key

dei_EntityCentralIndexKey

0000100334

Amendment Flag

dei_AmendmentFlag

false

Trading Symbol

dei_TradingSymbol

ACMF

Document Creation Date

dei_DocumentCreationDate

Feb. 27, 2015

Document Effective Date

dei_DocumentEffectiveDate

Mar. 01, 2015

Prospectus Date

rr_ProspectusDate

Mar. 01, 2015

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

All Cap Growth Fund (formerly known as Giftrust® 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 12 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 56% of the average value of its portfolio.   

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

56.00%

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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 of all sizes 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. 

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.

• Small and 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.

• 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): 18.71%Lowest Performance Quarter (4Q 2008): -26.56%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns  For the calendar year ended December 31, 2014

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 | ALL CAP GROWTH FUND | Russell 3000 Growth Index

Risk/Return:

rr_RiskReturnAbstract

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

   (reflects no deduction for fees, expenses or taxes)

Label

rr_AverageAnnualReturnLabel

Russell 3000® Growth Index    (reflects no deduction for fees, expenses or taxes)

1 Year

rr_AverageAnnualReturnYear01

12.44%

5 Years

rr_AverageAnnualReturnYear05

15.88%

10 Years

rr_AverageAnnualReturnYear10

8.49%

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWGTX

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 2005

rr_AnnualReturn2005

22.14%

Annual Return 2006

rr_AnnualReturn2006

17.21%

Annual Return 2007

rr_AnnualReturn2007

45.98%

Annual Return 2008

rr_AnnualReturn2008

(46.21%)

Annual Return 2009

rr_AnnualReturn2009

34.60%

Annual Return 2010

rr_AnnualReturn2010

22.48%

Annual Return 2011

rr_AnnualReturn2011

(3.16%)

Annual Return 2012

rr_AnnualReturn2012

15.71%

Annual Return 2013

rr_AnnualReturn2013

28.97%

Annual Return 2014

rr_AnnualReturn2014

9.70%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

18.71%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(26.56%)

Label

rr_AverageAnnualReturnLabel

Investor Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

9.70%

5 Years

rr_AverageAnnualReturnYear05

14.18%

10 Years

rr_AverageAnnualReturnYear10

11.37%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 25, 1983

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

5.95%

5 Years

rr_AverageAnnualReturnYear05

12.38%

10 Years

rr_AverageAnnualReturnYear10

10.49%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 25, 1983

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund  Shares

1 Year

rr_AverageAnnualReturnYear01

8.35%

5 Years

rr_AverageAnnualReturnYear05

11.36%

10 Years

rr_AverageAnnualReturnYear10

9.46%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 25, 1983

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACAJX

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

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

9.90%

Since Inception

rr_AverageAnnualReturnSinceInception

19.19%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2011

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACAQX

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

^[1]

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 Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.12%

5 Years

rr_AverageAnnualReturnYear05

12.55%

^[2]

10 Years

rr_AverageAnnualReturnYear10

10.44%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2011

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACAHX

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

8.58%

5 Years

rr_AverageAnnualReturnYear05

13.05%

^[2]

10 Years

rr_AverageAnnualReturnYear10

10.26%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2011

American Century Mutual Funds, Inc | ALL CAP GROWTH FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACAWX

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

9.14%

5 Years

rr_AverageAnnualReturnYear05

13.61%

^[2]

10 Years

rr_AverageAnnualReturnYear10

10.82%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 30, 2011

American Century Mutual Funds, Inc | BALANCED FUND

Risk/Return:

rr_RiskReturnAbstract

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 64% of the average value of its portfolio. 

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

64.00%

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example by Year [Heading]

rr_ExpenseExampleByYearHeading

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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 tied 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 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 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, 2014

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

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.

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

Risk/Return:

rr_RiskReturnAbstract

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

   (reflects no deduction for fees, expenses or taxes)

Label

rr_AverageAnnualReturnLabel

Barclays U.S. Aggregate Bond Index    (reflects no deduction for fees, expenses or taxes)

1 Year

rr_AverageAnnualReturnYear01

5.97%

5 Years

rr_AverageAnnualReturnYear05

4.45%

10 Years

rr_AverageAnnualReturnYear10

4.71%

American Century Mutual Funds, Inc | BALANCED FUND | Blended Index

Risk/Return:

rr_RiskReturnAbstract

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

10.62%

5 Years

rr_AverageAnnualReturnYear05

11.18%

10 Years

rr_AverageAnnualReturnYear10

6.77%

American Century Mutual Funds, Inc | BALANCED FUND | S&P 500 Index

Risk/Return:

rr_RiskReturnAbstract

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

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

10 Years

rr_AverageAnnualReturnYear10

7.67%

American Century Mutual Funds, Inc | BALANCED FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

92

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

287

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

499

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,108

Annual Return 2005

rr_AnnualReturn2005

4.80%

Annual Return 2006

rr_AnnualReturn2006

9.63%

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%

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

9.75%

5 Years

rr_AverageAnnualReturnYear05

11.07%

10 Years

rr_AverageAnnualReturnYear10

6.57%

American Century Mutual Funds, Inc | BALANCED FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

7.06%

5 Years

rr_AverageAnnualReturnYear05

9.54%

10 Years

rr_AverageAnnualReturnYear10

5.26%

American Century Mutual Funds, Inc | BALANCED FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

6.81%

5 Years

rr_AverageAnnualReturnYear05

8.49%

10 Years

rr_AverageAnnualReturnYear10

5.02%

American Century Mutual Funds, Inc | BALANCED FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ABINX

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.70%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

72

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

224

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

390

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

871

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.02%

5 Years

rr_AverageAnnualReturnYear05

11.30%

10 Years

rr_AverageAnnualReturnYear10

6.79%

American Century Mutual Funds, Inc | CAPITAL VALUE FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Capital Value 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 12 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 31% of the average value of its portfolio.   

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

31.00%

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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 use a value investment strategy that invests primarily in stocks of medium to large companies that the portfolio managers believe are undervalued at the time of purchase. In selecting stocks, the portfolio managers look for companies that are temporarily out of favor in, or whose value is not yet recognized by, the market. To identify these companies, the portfolio managers look for companies with earnings, cash flows and/or assets that may not be reflected accurately in the companies’ stock prices. 

The portfolio managers also attempt to minimize taxable distributions to fund shareholders. The fund’s tax-sensitive techniques may, from time to time, be inconsistent with the fund’s objective of long-term capital growth. Since the fund focuses on after-tax returns, it may not provide as high a pre-tax return relative to other funds. 

The portfolio managers may elect to sell a security, even if the sale results in a taxable gain, if they determine that the tax impact of the sale is outweighed by other factors. Such factors include the investment risk of holding the security or the availability of a replacement security that has a better potential return. 

Risk [Heading]

rr_RiskHeading

Principal Risks 

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

• Value Investing – If the market does not consider the individual stocks purchased by the fund to be undervalued, the value of the fund’s shares may decline, even if stock prices generally are rising.

• Tax Risk – While the fund seeks to minimize taxable distributions to shareholders, it nonetheless may realize capital gains on the sale of investment securities and earn dividend income. Federal tax laws require the fund to make distributions of such gains and income to its shareholders. Distributions may be taxable as ordinary income, capital gains, or a combination of the two.

• 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 (3Q 2009): 15.88%Lowest Performance Quarter (4Q 2008): -20.69%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns For the calendar year ended December 31, 2014

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 | CAPITAL VALUE FUND | Russell 1000 Growth Index

Risk/Return:

rr_RiskReturnAbstract

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

   (reflects no deduction for fees, expenses or taxes)

Label

rr_AverageAnnualReturnLabel

Russell 1000® Value Index    (reflects no deduction for fees, expenses or taxes)

1 Year

rr_AverageAnnualReturnYear01

13.45%

5 Years

rr_AverageAnnualReturnYear05

15.41%

10 Years

rr_AverageAnnualReturnYear10

7.30%

American Century Mutual Funds, Inc | CAPITAL VALUE FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACTIX

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

1.10%

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

1.10%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

112

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

350

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

607

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,340

Annual Return 2005

rr_AnnualReturn2005

3.70%

Annual Return 2006

rr_AnnualReturn2006

19.71%

Annual Return 2007

rr_AnnualReturn2007

(1.39%)

Annual Return 2008

rr_AnnualReturn2008

(36.84%)

Annual Return 2009

rr_AnnualReturn2009

19.32%

Annual Return 2010

rr_AnnualReturn2010

10.59%

Annual Return 2011

rr_AnnualReturn2011

1.22%

Annual Return 2012

rr_AnnualReturn2012

16.38%

Annual Return 2013

rr_AnnualReturn2013

31.32%

Annual Return 2014

rr_AnnualReturn2014

12.58%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.88%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(20.69%)

Label

rr_AverageAnnualReturnLabel

Investor Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

12.58%

5 Years

rr_AverageAnnualReturnYear05

14.00%

10 Years

rr_AverageAnnualReturnYear10

5.91%

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 31, 1999

American Century Mutual Funds, Inc | CAPITAL VALUE FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

10.61%

5 Years

rr_AverageAnnualReturnYear05

13.35%

10 Years

rr_AverageAnnualReturnYear10

5.35%

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 31, 1999

American Century Mutual Funds, Inc | CAPITAL VALUE FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

8.62%

5 Years

rr_AverageAnnualReturnYear05

11.24%

10 Years

rr_AverageAnnualReturnYear10

4.76%

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 31, 1999

American Century Mutual Funds, Inc | CAPITAL VALUE FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACPIX

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

0.90%

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

0.90%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

92

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

287

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

499

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,108

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

12.79%

5 Years

rr_AverageAnnualReturnYear05

14.26%

10 Years

rr_AverageAnnualReturnYear10

6.12%

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 01, 2002

American Century Mutual Funds, Inc | CAPITAL VALUE FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACCVX

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

^[1]

Maximum Account Fee

rr_MaximumAccountFee

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

1.10%

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

1.35%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

705

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

979

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,273

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,105

Label

rr_AverageAnnualReturnLabel

A Class1 Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.85%

^[3]

5 Years

rr_AverageAnnualReturnYear05

12.40%

^[3]

10 Years

rr_AverageAnnualReturnYear10

5.03%

^[3]

Inception Date

rr_AverageAnnualReturnInceptionDate

May 14, 2003

^[3]

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Focused 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 12 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 97% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

97.00%

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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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.

• 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.

• 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): 16.60%Lowest Performance Quarter (4Q 2008): -21.00%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns For the calendar year ended December 31, 2014

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 | FOCUSED GROWTH FUND | Russell 1000 Growth Index

Risk/Return:

rr_RiskReturnAbstract

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

13.05%

5 Years

rr_AverageAnnualReturnYear05

15.80%

Since Inception

rr_AverageAnnualReturnSinceInception

8.89%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2005

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFSIX

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 2006

rr_AnnualReturn2006

7.17%

Annual Return 2007

rr_AnnualReturn2007

13.04%

Annual Return 2008

rr_AnnualReturn2008

(36.06%)

Annual Return 2009

rr_AnnualReturn2009

33.43%

Annual Return 2010

rr_AnnualReturn2010

16.10%

Annual Return 2011

rr_AnnualReturn2011

(3.36%)

Annual Return 2012

rr_AnnualReturn2012

15.50%

Annual Return 2013

rr_AnnualReturn2013

29.49%

Annual Return 2014

rr_AnnualReturn2014

10.57%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

16.60%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.00%)

Label

rr_AverageAnnualReturnLabel

Investor Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.57%

5 Years

rr_AverageAnnualReturnYear05

13.15%

Since Inception

rr_AverageAnnualReturnSinceInception

7.75%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2005

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

4.97%

5 Years

rr_AverageAnnualReturnYear05

11.33%

Since Inception

rr_AverageAnnualReturnSinceInception

6.40%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2005

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

10.22%

5 Years

rr_AverageAnnualReturnYear05

10.42%

Since Inception

rr_AverageAnnualReturnSinceInception

6.05%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 28, 2005

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFGNX

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

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.72%

5 Years

rr_AverageAnnualReturnYear05

13.38%

Since Inception

rr_AverageAnnualReturnSinceInception

6.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFGAX

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

^[1]

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 Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.98%

5 Years

rr_AverageAnnualReturnYear05

11.56%

Since Inception

rr_AverageAnnualReturnSinceInception

5.63%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFGCX

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

9.41%

5 Years

rr_AverageAnnualReturnYear05

12.03%

Since Inception

rr_AverageAnnualReturnSinceInception

5.69%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | FOCUSED GROWTH FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFGRX

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

9.91%

5 Years

rr_AverageAnnualReturnYear05

12.57%

Since Inception

rr_AverageAnnualReturnSinceInception

6.22%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fundamental 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 12 of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information. The fund’s B Class shares are not available for purchase, except through exchanges and dividend reinvestments.

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 41% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

41.00%

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 12 of the fund’s prospectus and Sales Charges in Appendix B of the statement of additional information. The fund’s B Class shares are not available for purchase, except through exchanges and dividend reinvestments.

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 (unless otherwise indicated) and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above and B Class shares apply A Class operating expenses following the automatic conversion of such shares eight years after purchase. 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 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 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 tied 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.

• 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, 2014

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 | FUNDAMENTAL EQUITY FUND | S&P 500 Index

Risk/Return:

rr_RiskReturnAbstract

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

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

10 Years

rr_AverageAnnualReturnYear10

7.67%

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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

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

Label

rr_AverageAnnualReturnLabel

Investor Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

14.07%

5 Years

rr_AverageAnnualReturnYear05

15.45%

Since Inception

rr_AverageAnnualReturnSinceInception

9.56%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 29, 2005

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFEIX

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

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

14.23%

5 Years

rr_AverageAnnualReturnYear05

15.67%

Since Inception

rr_AverageAnnualReturnSinceInception

9.77%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 29, 2005

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

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

^[1]

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

Annual Return 2005

rr_AnnualReturn2005

10.94%

Annual Return 2006

rr_AnnualReturn2006

20.64%

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%

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

7.17%

5 Years

rr_AverageAnnualReturnYear05

13.80%

10 Years

rr_AverageAnnualReturnYear10

8.59%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | A CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

6.91%

5 Years

rr_AverageAnnualReturnYear05

13.59%

10 Years

rr_AverageAnnualReturnYear10

8.22%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | A CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

4.25%

5 Years

rr_AverageAnnualReturnYear05

11.09%

10 Years

rr_AverageAnnualReturnYear10

6.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | B CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AFDBX

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

5.00%

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

603

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

928

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,179

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,132

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

203

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

628

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,079

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,132

Label

rr_AverageAnnualReturnLabel

B Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

8.89%

5 Years

rr_AverageAnnualReturnYear05

14.17%

10 Years

rr_AverageAnnualReturnYear10

8.41%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

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

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

12.89%

5 Years

rr_AverageAnnualReturnYear05

14.28%

10 Years

rr_AverageAnnualReturnYear10

8.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

American Century Mutual Funds, Inc | FUNDAMENTAL EQUITY FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

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

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

13.46%

5 Years

rr_AverageAnnualReturnYear05

14.85%

Since Inception

rr_AverageAnnualReturnSinceInception

9.00%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 29, 2005

American Century Mutual Funds, Inc | GROWTH FUND

Risk/Return:

rr_RiskReturnAbstract

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 12 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 103% of the average value of its portfolio.   

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

103.00%

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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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, 2014

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

Risk/Return:

rr_RiskReturnAbstract

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

13.05%

5 Years

rr_AverageAnnualReturnYear05

15.80%

10 Years

rr_AverageAnnualReturnYear10

8.49%

American Century Mutual Funds, Inc | GROWTH FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.97%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

99

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

310

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

537

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,190

Annual Return 2005

rr_AnnualReturn2005

4.84%

Annual Return 2006

rr_AnnualReturn2006

7.94%

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%

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

11.22%

5 Years

rr_AverageAnnualReturnYear05

13.82%

10 Years

rr_AverageAnnualReturnYear10

8.03%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 1971

American Century Mutual Funds, Inc | GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

5.42%

5 Years

rr_AverageAnnualReturnYear05

11.99%

10 Years

rr_AverageAnnualReturnYear10

7.14%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 1971

American Century Mutual Funds, Inc | GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

10.29%

5 Years

rr_AverageAnnualReturnYear05

10.97%

10 Years

rr_AverageAnnualReturnYear10

6.49%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 1971

American Century Mutual Funds, Inc | GROWTH FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWGIX

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.77%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

79

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

246

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

428

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

955

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

11.41%

5 Years

rr_AverageAnnualReturnYear05

14.04%

10 Years

rr_AverageAnnualReturnYear10

8.25%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 16, 1997

American Century Mutual Funds, Inc | GROWTH FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

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

^[1]

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.22%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

692

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

941

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,207

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,967

Label

rr_AverageAnnualReturnLabel

A Class1 Return Before Taxes

^[3]

1 Year

rr_AverageAnnualReturnYear01

4.54%

5 Years

rr_AverageAnnualReturnYear05

12.21%

10 Years

rr_AverageAnnualReturnYear10

7.13%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 04, 1997

American Century Mutual Funds, Inc | GROWTH FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.97%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

200

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

619

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,063

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,293

Label

rr_AverageAnnualReturnLabel

C Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.08%

5 Years

rr_AverageAnnualReturnYear05

12.68%

^[4]

10 Years

rr_AverageAnnualReturnYear10

6.96%

^[4]

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 01, 2010

American Century Mutual Funds, Inc | GROWTH FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.47%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

150

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

466

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

803

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,756

Label

rr_AverageAnnualReturnLabel

R Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.64%

5 Years

rr_AverageAnnualReturnYear05

13.25%

10 Years

rr_AverageAnnualReturnYear10

7.50%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 29, 2003

American Century Mutual Funds, Inc | GROWTH FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.62%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

63

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

199

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

346

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

775

Label

rr_AverageAnnualReturnLabel

R6 Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

11.56%

Since Inception

rr_AverageAnnualReturnSinceInception

17.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | HERITAGE FUND

Risk/Return:

rr_RiskReturnAbstract

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 and Sales Charges in Appendix B of the statement of additional information. The fund’s B Class shares are not available for purchase, except through exchanges and dividend reinvestments.      

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 73% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

73.00%

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 and Sales Charges in Appendix B of the statement of additional information. The fund’s B Class shares are not available for purchase, except through exchanges and dividend reinvestments.      

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 (unless otherwise indicated) and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above and B Class shares apply A Class operating expenses following the automatic conversion of such shares eight years after purchase. 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 can 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, 2014

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

Risk/Return:

rr_RiskReturnAbstract

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

11.90%

5 Years

rr_AverageAnnualReturnYear05

16.93%

10 Years

rr_AverageAnnualReturnYear10

9.42%

American Century Mutual Funds, Inc | HERITAGE FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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 2005

rr_AnnualReturn2005

22.23%

Annual Return 2006

rr_AnnualReturn2006

17.05%

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%

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

8.16%

5 Years

rr_AverageAnnualReturnYear05

15.08%

10 Years

rr_AverageAnnualReturnYear10

11.98%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 10, 1987

American Century Mutual Funds, Inc | HERITAGE FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

4.39%

5 Years

rr_AverageAnnualReturnYear05

13.49%

10 Years

rr_AverageAnnualReturnYear10

10.99%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 10, 1987

American Century Mutual Funds, Inc | HERITAGE FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

7.48%

5 Years

rr_AverageAnnualReturnYear05

12.07%

10 Years

rr_AverageAnnualReturnYear10

9.95%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 10, 1987

American Century Mutual Funds, Inc | HERITAGE FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ATHIX

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

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

8.36%

5 Years

rr_AverageAnnualReturnYear05

15.30%

10 Years

rr_AverageAnnualReturnYear10

12.20%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 16, 1997

American Century Mutual Funds, Inc | HERITAGE FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

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

^[1]

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 Class1 Return Before Taxes

^[5]

1 Year

rr_AverageAnnualReturnYear01

1.69%

5 Years

rr_AverageAnnualReturnYear05

13.43%

10 Years

rr_AverageAnnualReturnYear10

11.04%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 11, 1997

American Century Mutual Funds, Inc | HERITAGE FUND | B CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ATHBX

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

5.00%

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

603

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

928

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,179

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,132

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

203

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

628

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,079

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,132

Label

rr_AverageAnnualReturnLabel

B Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.08%

5 Years

rr_AverageAnnualReturnYear05

13.82%

Since Inception

rr_AverageAnnualReturnSinceInception

5.55%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | HERITAGE FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

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

7.11%

5 Years

rr_AverageAnnualReturnYear05

13.94%

10 Years

rr_AverageAnnualReturnYear10

10.87%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 26, 2001

American Century Mutual Funds, Inc | HERITAGE FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

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

7.64%

5 Years

rr_AverageAnnualReturnYear05

14.51%

Since Inception

rr_AverageAnnualReturnSinceInception

6.07%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | HERITAGE FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

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

8.55%

Since Inception

rr_AverageAnnualReturnSinceInception

13.44%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

New Opportunities 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 12 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 76% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

76.00%

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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 small and mid-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 and Mid Cap Stocks – The smaller and medium-sized 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.

• 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 2009): 19.10%Lowest Performance Quarter (4Q 2008): -25.16%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns   For the calendar year ended December 31, 2014

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 | NEW OPPORTUNITIES FUND | Russell 2500 Growth Index

Risk/Return:

rr_RiskReturnAbstract

Index No Deduction for Fees, Expenses, Taxes [Text]

rr_IndexNoDeductionForFeesExpensesTaxes

   (reflects no deduction for fees, expenses or taxes)

Label

rr_AverageAnnualReturnLabel

Russell 2500® Growth Index    (reflects no deduction for fees, expenses or taxes)

1 Year

rr_AverageAnnualReturnYear01

7.05%

5 Years

rr_AverageAnnualReturnYear05

17.26%

10 Years

rr_AverageAnnualReturnYear10

9.36%

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWNOX

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

1.50%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.51%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

154

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

478

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

824

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,800

Annual Return 2005

rr_AnnualReturn2005

6.82%

Annual Return 2006

rr_AnnualReturn2006

10.76%

Annual Return 2007

rr_AnnualReturn2007

23.07%

Annual Return 2008

rr_AnnualReturn2008

(42.42%)

Annual Return 2009

rr_AnnualReturn2009

26.34%

Annual Return 2010

rr_AnnualReturn2010

29.32%

Annual Return 2011

rr_AnnualReturn2011

(4.19%)

Annual Return 2012

rr_AnnualReturn2012

14.50%

Annual Return 2013

rr_AnnualReturn2013

38.11%

Annual Return 2014

rr_AnnualReturn2014

5.48%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

19.10%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.16%)

Label

rr_AverageAnnualReturnLabel

Investor Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.48%

5 Years

rr_AverageAnnualReturnYear05

15.62%

10 Years

rr_AverageAnnualReturnYear10

8.15%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 26, 1996

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

3.85%

5 Years

rr_AverageAnnualReturnYear05

15.26%

10 Years

rr_AverageAnnualReturnYear10

7.98%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 26, 1996

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

4.34%

5 Years

rr_AverageAnnualReturnYear05

12.60%

10 Years

rr_AverageAnnualReturnYear10

6.65%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 26, 1996

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWNIX

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

1.30%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.31%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

134

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

416

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

719

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,578

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.70%

Since Inception

rr_AverageAnnualReturnSinceInception

15.74%

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 01, 2010

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWNAX

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

^[1]

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

1.50%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.76%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

744

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,098

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,475

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,527

Label

rr_AverageAnnualReturnLabel

A Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.79%)

5 Years

rr_AverageAnnualReturnYear05

13.99%

^[2]

10 Years

rr_AverageAnnualReturnYear10

7.26%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 01, 2010

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWNCX

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

1.50%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

2.51%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

255

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

783

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,336

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,841

Label

rr_AverageAnnualReturnLabel

C Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

4.44%

5 Years

rr_AverageAnnualReturnYear05

14.46%

^[2]

10 Years

rr_AverageAnnualReturnYear10

7.06%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 01, 2010

American Century Mutual Funds, Inc | NEW OPPORTUNITIES FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWNRX

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

1.50%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

2.01%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

204

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

632

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,084

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,334

Label

rr_AverageAnnualReturnLabel

R Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

4.97%

5 Years

rr_AverageAnnualReturnYear05

15.06%

^[2]

10 Years

rr_AverageAnnualReturnYear10

7.60%

^[2]

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 01, 2010

American Century Mutual Funds, Inc | NT GROWTH FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

NT 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.

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 119% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

119.00%

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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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.      

The fund is not permitted to invest in securities issued by companies assigned the Global Industry Classification Standard (GICS) for the tobacco industry.

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.

• Tobacco Exclusion – The fund’s prohibition on tobacco-related investments may cause it to forego profitable investment opportunities.

• 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) 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 Institutional 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.

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 Institutional 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 Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Performance Quarter (2Q 2009): 15.77%Lowest Performance Quarter (4Q 2008): -22.96%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns For the calendar year ended December 31, 2014

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The 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 Institutional 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 Institutional Class shares. After-tax returns for other share classes will vary. The 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 | NT GROWTH FUND | Russell 1000 Growth Index

Risk/Return:

rr_RiskReturnAbstract

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

13.05%

5 Years

rr_AverageAnnualReturnYear05

15.80%

Since Inception

rr_AverageAnnualReturnSinceInception

9.08%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT GROWTH FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACLTX

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.77%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

79

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

246

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

428

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

955

Annual Return 2007

rr_AnnualReturn2007

19.08%

Annual Return 2008

rr_AnnualReturn2008

(37.68%)

Annual Return 2009

rr_AnnualReturn2009

36.21%

Annual Return 2010

rr_AnnualReturn2010

17.94%

Annual Return 2011

rr_AnnualReturn2011

(0.79%)

Annual Return 2012

rr_AnnualReturn2012

13.84%

Annual Return 2013

rr_AnnualReturn2013

30.10%

Annual Return 2014

rr_AnnualReturn2014

11.49%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

15.77%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(22.96%)

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

11.49%

5 Years

rr_AverageAnnualReturnYear05

14.07%

Since Inception

rr_AverageAnnualReturnSinceInception

8.89%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT GROWTH FUND | INSTITUTIONAL CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

7.17%

5 Years

rr_AverageAnnualReturnYear05

12.66%

Since Inception

rr_AverageAnnualReturnSinceInception

7.95%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT GROWTH FUND | INSTITUTIONAL CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

9.26%

5 Years

rr_AverageAnnualReturnYear05

11.20%

Since Inception

rr_AverageAnnualReturnSinceInception

7.12%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT GROWTH FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACDTX

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

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.62%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

63

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

199

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

346

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

775

Label

rr_AverageAnnualReturnLabel

R6 Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

11.68%

Since Inception

rr_AverageAnnualReturnSinceInception

17.52%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | NT HERITAGE FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

NT 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.

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 76% of the average value of its portfolio.   

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

76.00%

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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 primarily 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 can 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 is not permitted to invest in securities issued by companies assigned the Global Industry Classification Standard (GICS) for the tobacco industry.

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.

• Tobacco Exclusion – The fund’s prohibition on tobacco-related investments may cause it to forego profitable investment opportunities.

• 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.

• 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.

• 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) 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 Institutional 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.

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 Institutional 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 Closing [Text Block]

rr_BarChartClosingTextBlock

Highest Performance Quarter (1Q 2012): 16.67%Lowest Performance Quarter (4Q 2008): -25.63%

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns For the calendar year ended December 31, 2014

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

The 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 Institutional 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 Institutional Class shares. After-tax returns for other share classes will vary. The 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 | NT HERITAGE FUND | Russell Midcap Growth Index

Risk/Return:

rr_RiskReturnAbstract

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

11.90%

5 Years

rr_AverageAnnualReturnYear05

16.93%

Since Inception

rr_AverageAnnualReturnSinceInception

8.72%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT HERITAGE FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACLWX

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

Annual Return 2007

rr_AnnualReturn2007

38.04%

Annual Return 2008

rr_AnnualReturn2008

(48.05%)

Annual Return 2009

rr_AnnualReturn2009

22.69%

Annual Return 2010

rr_AnnualReturn2010

24.25%

Annual Return 2011

rr_AnnualReturn2011

(7.43%)

Annual Return 2012

rr_AnnualReturn2012

15.58%

Annual Return 2013

rr_AnnualReturn2013

30.45%

Annual Return 2014

rr_AnnualReturn2014

8.32%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2012

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

16.67%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.63%)

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

8.32%

5 Years

rr_AverageAnnualReturnYear05

13.43%

Since Inception

rr_AverageAnnualReturnSinceInception

5.35%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT HERITAGE FUND | INSTITUTIONAL CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

7.09%

5 Years

rr_AverageAnnualReturnYear05

12.45%

Since Inception

rr_AverageAnnualReturnSinceInception

4.82%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT HERITAGE FUND | INSTITUTIONAL CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

5.64%

5 Years

rr_AverageAnnualReturnYear05

10.65%

Since Inception

rr_AverageAnnualReturnSinceInception

4.18%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 12, 2006

American Century Mutual Funds, Inc | NT HERITAGE FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ACDUX

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

8.47%

Since Inception

rr_AverageAnnualReturnSinceInception

13.00%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | SELECT FUND

Risk/Return:

rr_RiskReturnAbstract

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 12 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 25% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

25.00%

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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 fund’s portfolio will primarily consist of securities of companies whose earnings or revenues 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. 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. 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, 2014

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

Risk/Return:

rr_RiskReturnAbstract

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

13.05%

5 Years

rr_AverageAnnualReturnYear05

15.80%

10 Years

rr_AverageAnnualReturnYear10

8.49%

American Century Mutual Funds, Inc | SELECT FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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

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 2005

rr_AnnualReturn2005

0.86%

Annual Return 2006

rr_AnnualReturn2006

(1.79%)

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%

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

10.52%

5 Years

rr_AverageAnnualReturnYear05

13.92%

10 Years

rr_AverageAnnualReturnYear10

6.52%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 1971

American Century Mutual Funds, Inc | SELECT FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

8.03%

5 Years

rr_AverageAnnualReturnYear05

13.31%

10 Years

rr_AverageAnnualReturnYear10

6.00%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 1971

American Century Mutual Funds, Inc | SELECT FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

7.88%

5 Years

rr_AverageAnnualReturnYear05

11.16%

10 Years

rr_AverageAnnualReturnYear10

5.21%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 30, 1971

American Century Mutual Funds, Inc | SELECT FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWSIX

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

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.73%

5 Years

rr_AverageAnnualReturnYear05

14.15%

10 Years

rr_AverageAnnualReturnYear10

6.73%

Inception Date

rr_AverageAnnualReturnInceptionDate

Mar. 13, 1997

American Century Mutual Funds, Inc | SELECT FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

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

^[1]

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 Class1 Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.90%

^[5]

5 Years

rr_AverageAnnualReturnYear05

12.29%

^[5]

10 Years

rr_AverageAnnualReturnYear10

5.63%

^[5]

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 08, 1997

^[5]

American Century Mutual Funds, Inc | SELECT FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

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

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

9.40%

5 Years

rr_AverageAnnualReturnYear05

12.78%

10 Years

rr_AverageAnnualReturnYear10

5.46%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2003

American Century Mutual Funds, Inc | SELECT FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

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

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

9.96%

5 Years

rr_AverageAnnualReturnYear05

13.34%

Since Inception

rr_AverageAnnualReturnSinceInception

6.32%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 29, 2005

American Century Mutual Funds, Inc | SELECT FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

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

0.65%

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

10.92%

Since Inception

rr_AverageAnnualReturnSinceInception

18.63%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND

Risk/Return:

rr_RiskReturnAbstract

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 and Sales Charges in Appendix B of the statement of additional information. The fund’s B Class shares are not available for purchase, except through exchanges and dividend reinvestments.

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 75% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

75.00%

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 and Sales Charges in Appendix B of the statement of additional information. The fund’s B Class shares are not available for purchase, except through exchanges and dividend reinvestments.       

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 (unless otherwise indicated) and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above and B Class shares apply A Class operating expenses following the automatic conversion of such shares eight years after purchase. 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.

• 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, 2014

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

Risk/Return:

rr_RiskReturnAbstract

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

5.60%

5 Years

rr_AverageAnnualReturnYear05

16.79%

10 Years

rr_AverageAnnualReturnYear10

8.54%

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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

1.40%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.41%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

144

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

447

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

772

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,690

Annual Return 2005

rr_AnnualReturn2005

5.06%

Annual Return 2006

rr_AnnualReturn2006

13.64%

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%

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

5.45%

5 Years

rr_AverageAnnualReturnYear05

15.97%

10 Years

rr_AverageAnnualReturnYear10

8.42%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 01, 2001

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

5.45%

5 Years

rr_AverageAnnualReturnYear05

15.96%

10 Years

rr_AverageAnnualReturnYear10

8.16%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 01, 2001

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

3.08%

5 Years

rr_AverageAnnualReturnYear05

12.93%

10 Years

rr_AverageAnnualReturnYear10

6.83%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jun. 01, 2001

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ANONX

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

1.20%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.21%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

124

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

385

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

666

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,465

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.69%

5 Years

rr_AverageAnnualReturnYear05

16.18%

Since Inception

rr_AverageAnnualReturnSinceInception

6.86%

Inception Date

rr_AverageAnnualReturnInceptionDate

May 18, 2007

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

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

^[1]

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

1.40%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.66%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

734

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,069

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,426

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,426

Label

rr_AverageAnnualReturnLabel

A Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

(0.91%)

5 Years

rr_AverageAnnualReturnYear05

14.27%

10 Years

rr_AverageAnnualReturnYear10

7.53%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2003

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | B CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

ANOBX

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

5.00%

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

1.40%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

2.41%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

645

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

1,053

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,386

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,557

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

245

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

753

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

1,286

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

2,557

Label

rr_AverageAnnualReturnLabel

B Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

0.35%

5 Years

rr_AverageAnnualReturnYear05

14.71%

10 Years

rr_AverageAnnualReturnYear10

7.35%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2003

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

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

1.40%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

2.41%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

245

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

753

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,286

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,742

Label

rr_AverageAnnualReturnLabel

C Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

4.42%

5 Years

rr_AverageAnnualReturnYear05

14.81%

10 Years

rr_AverageAnnualReturnYear10

7.36%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jan. 31, 2003

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

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

1.40%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.91%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

194

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

601

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,032

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,230

Label

rr_AverageAnnualReturnLabel

R Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

4.88%

5 Years

rr_AverageAnnualReturnYear05

15.38%

Since Inception

rr_AverageAnnualReturnSinceInception

5.19%

Inception Date

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2007

American Century Mutual Funds, Inc | SMALL CAP GROWTH FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

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

1.05%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

none

Acquired Fund Fees and Expenses

rr_AcquiredFundFeesAndExpensesOverAssets

0.01%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.06%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

108

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

338

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

585

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,294

Label

rr_AverageAnnualReturnLabel

R6 Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

5.76%

Since Inception

rr_AverageAnnualReturnSinceInception

13.48%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | ULTRA FUND

Risk/Return:

rr_RiskReturnAbstract

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 12 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 12 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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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 fund’s portfolio will primarily consist of securities of companies whose earnings or revenues 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. 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, 2014

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

Risk/Return:

rr_RiskReturnAbstract

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

13.05%

5 Years

rr_AverageAnnualReturnYear05

15.80%

10 Years

rr_AverageAnnualReturnYear10

8.49%

American Century Mutual Funds, Inc | ULTRA FUND | S&P 500 Index

Risk/Return:

rr_RiskReturnAbstract

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

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

10 Years

rr_AverageAnnualReturnYear10

7.67%

American Century Mutual Funds, Inc | ULTRA FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

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

0.03%

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

Annual Return 2005

rr_AnnualReturn2005

2.12%

Annual Return 2006

rr_AnnualReturn2006

(3.28%)

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%

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

9.91%

5 Years

rr_AverageAnnualReturnYear05

15.17%

10 Years

rr_AverageAnnualReturnYear10

6.75%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 02, 1981

American Century Mutual Funds, Inc | ULTRA FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

7.99%

5 Years

rr_AverageAnnualReturnYear05

14.51%

10 Years

rr_AverageAnnualReturnYear10

5.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 02, 1981

American Century Mutual Funds, Inc | ULTRA FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

7.09%

5 Years

rr_AverageAnnualReturnYear05

12.20%

10 Years

rr_AverageAnnualReturnYear10

5.46%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 02, 1981

American Century Mutual Funds, Inc | ULTRA FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

TWUIX

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

0.03%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.81%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

83

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

259

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

450

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,002

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.14%

5 Years

rr_AverageAnnualReturnYear05

15.40%

10 Years

rr_AverageAnnualReturnYear10

6.97%

Inception Date

rr_AverageAnnualReturnInceptionDate

Nov. 14, 1996

American Century Mutual Funds, Inc | ULTRA FUND | A CLASS

Risk/Return:

rr_RiskReturnAbstract

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

^[1]

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

0.03%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.26%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

696

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

952

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,228

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,010

Label

rr_AverageAnnualReturnLabel

A Class1 Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

3.31%

^[5]

5 Years

rr_AverageAnnualReturnYear05

13.53%

^[5]

10 Years

rr_AverageAnnualReturnYear10

5.86%

^[5]

Inception Date

rr_AverageAnnualReturnInceptionDate

Oct. 02, 1996

American Century Mutual Funds, Inc | ULTRA FUND | C CLASS

Risk/Return:

rr_RiskReturnAbstract

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

0.03%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

2.01%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

204

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

632

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

1,084

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

2,334

Label

rr_AverageAnnualReturnLabel

C Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

8.83%

5 Years

rr_AverageAnnualReturnYear05

14.03%

10 Years

rr_AverageAnnualReturnYear10

5.69%

Inception Date

rr_AverageAnnualReturnInceptionDate

Oct. 29, 2001

American Century Mutual Funds, Inc | ULTRA FUND | R CLASS

Risk/Return:

rr_RiskReturnAbstract

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

0.03%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.51%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

154

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

478

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

824

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,800

Label

rr_AverageAnnualReturnLabel

R Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

9.36%

5 Years

rr_AverageAnnualReturnYear05

14.58%

10 Years

rr_AverageAnnualReturnYear10

6.22%

Inception Date

rr_AverageAnnualReturnInceptionDate

Aug. 29, 2003

American Century Mutual Funds, Inc | ULTRA FUND | R6 CLASS

Risk/Return:

rr_RiskReturnAbstract

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

0.03%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.66%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

68

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

212

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

368

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

823

Label

rr_AverageAnnualReturnLabel

R6 Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.28%

Since Inception

rr_AverageAnnualReturnSinceInception

18.79%

Inception Date

rr_AverageAnnualReturnInceptionDate

Jul. 26, 2013

American Century Mutual Funds, Inc | VEEDOT FUND

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Veedot® 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]

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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]

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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 184% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

184.00%

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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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 and that you earn a 5% return each year. The example also assumes that the fund’s operating expenses remain the same, except that it reflects the rate and duration of any fee waivers noted in the table above. 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]

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The portfolio managers look for stocks of 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, revenues and/or cash flow.

The portfolio managers use an approach to common stock investing that relies heavily on quantitative tools to identify companies, regardless of size, industry type or geographic location, whose share price patterns suggest their stocks are likely to increase in value. This technical analysis is particularly oriented to identifying attractive price patterns for companies whose earnings and revenues 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. These companies would be candidates for purchase. Conversely, companies whose share price patterns suggest a likely decline in price would be candidates for sale, if owned by the fund. On occasion, the process may look favorably on a company whose share price pattern appears attractive even though the company looks less attractive based on the growth screen.

The fund may engage in active and frequent trading of portfolio securities to achieve its principal investment strategy. This may cause higher transaction costs and may affect performance. It may also result in the realization and distribution of capital gains.

The process driving the fund is specifically designed to respond quickly to changing stock market conditions. As a result, the fund’s portfolio turnover, perhaps as much as 200-400% per year or more, may be significantly higher than that of many other funds.

In addition to investing in U.S. companies, the fund may invest in securities of foreign companies, including companies located in emerging markets when these securities meet the portfolio managers’ standards of selection.

Risk [Heading]

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Principal Risks 

Risk Narrative [Text Block]

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• 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.

• Investment Process – There is also risk associated with reliance on the fund’s computer-based investment process. If the investment style embedded in this process falls out of favor with the market, the fund’s performance may suffer.

• Nondiversification – The fund is classified as nondiversified. This gives the portfolio managers the flexibility to hold large positions in a small number of securities. If so, a price change in any one of those securities may have a greater impact on the fund’s share prices than would be the case in a diversified fund.

• 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. Investing in securities of companies located in emerging market countries generally is also riskier than investing in securities of companies located in foreign developed countries.

• 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]

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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 Nondiversified Status [Text]

rr_RiskNondiversifiedStatus

Nondiversification – The fund is classified as nondiversified. This gives the portfolio managers the flexibility to hold large positions in a small number of securities. If so, a price change in any one of those securities may have a greater impact on the fund’s share prices than would be the case in a diversified fund.

Risk Not Insured Depository Institution [Text]

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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]

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Fund Performance

Performance Narrative [Text Block]

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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]

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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]

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Calendar Year Total Returns

Bar Chart Does Not Reflect Sales Loads [Text]

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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]

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Highest Performance Quarter (3Q 2009): 18.92%Lowest Performance Quarter (3Q 2008): -25.25%

Performance Table Heading

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Average Annual Total Returns  For the calendar year ended December 31, 2014

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]

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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]

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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 | VEEDOT FUND | Russell 3000 Index

Risk/Return:

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Index No Deduction for Fees, Expenses, Taxes [Text]

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   (reflects no deduction for fees, expenses or taxes)

Label

rr_AverageAnnualReturnLabel

Russell 3000® Index    (reflects no deduction for fees, expenses or taxes)

1 Year

rr_AverageAnnualReturnYear01

12.56%

5 Years

rr_AverageAnnualReturnYear05

15.62%

10 Years

rr_AverageAnnualReturnYear10

7.94%

American Century Mutual Funds, Inc | VEEDOT FUND | INVESTOR CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AMVIX

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

1.25%

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

1.25%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

128

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

397

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

687

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,511

Annual Return 2005

rr_AnnualReturn2005

5.42%

Annual Return 2006

rr_AnnualReturn2006

10.10%

Annual Return 2007

rr_AnnualReturn2007

32.04%

Annual Return 2008

rr_AnnualReturn2008

(41.70%)

Annual Return 2009

rr_AnnualReturn2009

8.55%

Annual Return 2010

rr_AnnualReturn2010

13.35%

Annual Return 2011

rr_AnnualReturn2011

4.98%

Annual Return 2012

rr_AnnualReturn2012

11.31%

Annual Return 2013

rr_AnnualReturn2013

39.00%

Annual Return 2014

rr_AnnualReturn2014

10.45%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Performance Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Sep. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

18.92%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Performance Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(25.25%)

Label

rr_AverageAnnualReturnLabel

Investor Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.45%

5 Years

rr_AverageAnnualReturnYear05

15.24%

10 Years

rr_AverageAnnualReturnYear10

7.02%

American Century Mutual Funds, Inc | VEEDOT FUND | INVESTOR CLASS | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

1 Year

rr_AverageAnnualReturnYear01

10.30%

5 Years

rr_AverageAnnualReturnYear05

15.02%

10 Years

rr_AverageAnnualReturnYear10

6.92%

American Century Mutual Funds, Inc | VEEDOT FUND | INVESTOR CLASS | After Taxes on Distributions and Sales

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

1 Year

rr_AverageAnnualReturnYear01

6.03%

5 Years

rr_AverageAnnualReturnYear05

12.30%

10 Years

rr_AverageAnnualReturnYear10

5.69%

American Century Mutual Funds, Inc | VEEDOT FUND | INSTITUTIONAL CLASS

Risk/Return:

rr_RiskReturnAbstract

Trading Symbol

dei_TradingSymbol

AVDIX

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

1.05%

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

1.05%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

107

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

335

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

580

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,282

Label

rr_AverageAnnualReturnLabel

Institutional Class Return Before Taxes

1 Year

rr_AverageAnnualReturnYear01

10.56%

5 Years

rr_AverageAnnualReturnYear05

15.47%

10 Years

rr_AverageAnnualReturnYear10

7.25%

[1] 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.

[2] Historical performance for A, C and R Classes prior to their inception is based on the performance of Investor Class shares. A, C and R Class performance has been adjusted to reflect differences in sales charges, if applicable, and expenses between classes.

[3] 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.

[4] 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.

[5] 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.