Label

Element

Value

Prospectus:

rr_ProspectusTable

Document Type

dei_DocumentType

497

Document Period End Date

dei_DocumentPeriodEndDate

Mar. 19, 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

Mar. 19, 2020

Document Effective Date

dei_DocumentEffectiveDate

Mar. 19, 2020

Prospectus Date

rr_ProspectusDate

Mar. 19, 2020

AMERICAN CENTURY CALIFORNIA TAX FREE & MUNICIPAL FUNDS

Prospectus:

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Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century ETF Trust

Prospectus:

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Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Target Maturities Trust

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Mutual Funds, Inc

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Capital Portfolios Prospectus

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century International Bond Fund

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

AMERICAN CENTURY WORLD MUTUAL FUNDS INC

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

AMERICAN CENTURY VARIABLE PORTFOLIOS INC

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

AMERICAN CENTURY VARIABLE PORTFOLIOS II INC

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Government Income Trust

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

AMERICAN CENTURY INVESTMENT TRUST

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

AMERICAN CENTURY MUNICIPAL TRUST

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Quantitative Equity Funds Prospectus

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Asset Allocation Portfolio

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

American Century Growth Funds

Prospectus:

rr_ProspectusTable

Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.

AMERICAN CENTURY STRATEGIC ASSET ALLOCATIONS

Prospectus:

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Supplement [Text Block]

ck000077367_SupplementTextBlock

Summary Prospectus and Prospectus Supplement

Supplement dated March 19, 2020

American Century California Tax-Free and Municipal Funds n American Century ETF Trust

American Century Target Maturities Trust n American Century Mutual Funds, Inc.

American Century Capital Portfolios, Inc. n American Century International Bond Funds

American Century World Mutual Funds, Inc. n American Century Variable Portfolios, Inc.

American Century Variable Portfolios II, Inc. n American Century Government Income Trust

American Century Investment Trust n American Century Municipal Trust

American Century Quantitative Equity Funds, Inc. n American Century Asset Allocation Portfolios, Inc.

American Century Growth Funds, Inc. n American Century Strategic Asset Allocations, Inc.

The following disclosure is added to the Market Risk in the Principal Risks section in each summary prospectus and prospectus, as well as the section titled What are the principal risks of investing in the fund?, ineach prospectus:

Market risks, including political, regulatory, economic and social developments, can affect the value of the fund’s investments. Natural disasters, public health emergencies, terrorism and other unforeseeable events may lead to increased market volatility and may have adverse long-term effects on world economies and markets generally.