Label

Element

Value

Prospectus:

rr_ProspectusTable

Document Type

dei_DocumentType

497

Document Period End Date

dei_DocumentPeriodEndDate

Jul. 31, 2020

Entity Registrant Name

dei_EntityRegistrantName

AMERICAN CENTURY MUTUAL FUNDS, INC.

Central Index Key

dei_EntityCentralIndexKey

0000100334

Amendment Flag

dei_AmendmentFlag

false

Document Creation Date

dei_DocumentCreationDate

Jul. 31, 2020

Document Effective Date

dei_DocumentEffectiveDate

Mar. 01, 2020

Prospectus Date

rr_ProspectusDate

Mar. 01, 2020

American Century Mutual Funds, Inc | BALANCED FUND

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck0000100334_SupplementTextBlock

American Century Mutual Funds, Inc.

Summary Prospectus and Prospectus Supplement

Balanced Fund

Supplement dated August 1, 2020 n Summary Prospectus and Prospectus dated March 1, 2020

The following replaces the first paragraph of the Principal Investment Strategies section on page 2 of the summary prospectus and prospectus:

For the equity portion of the fund, the portfolio managers select stocks using quantitative management techniques in a multi-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. Finally, the portfolio managers review the output of the quantitative model, considering factors such as risk management, transaction costs, and liquidity management.