Acquisitions and Sale of Businesses (Details 1) (Run-off long-term care insurance business [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Run-off long-term care insurance business [Member]
Life, accident and health net earned premiums:
Long-term care	$ 17	$ 19
Life operations	3	3
Net investment income	18	21
Realized gains (losses) on securities and other income	(2)	1
Total revenues	36	44
Annuity benefits	2	2
Life, accident and health benefits:
Long-term care	21	29
Life operations	3	3
Annuity and supplemental insurance acquisition expenses	3	3
Other expenses	4	4
Total costs and expenses	33	41
Earnings before income taxes	$ 3	$ 3

Annuity and supplemental insurance acquisition expenses of the disposal group.

No definition available.

Name:	afg_DisposalGroupAnnuityandSupplementalInsuranceAcquisitionExpenses
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Annuity benefits of the disposal group includes 1) interest credited to policyholders accounts, which provides a guaranteed yield, 2) expenses related to excess benefits expected to be paid on future deaths and annuitizations and 3) net expenses related to changes in embedded derivatives on equity indexed annuities offset by equity index call options.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupAnnuityBenefits
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The Life operations portion of life, accident and health benefits of the disposal group.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupLifeAccidentandHealthBenefitsLifeOperations
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The Long-term care portion of life, accident and health benefits of the disposal group.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupLifeAccidentandHealthBenefitsLongTermCare
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The Life operations portion of life, accident and health premiums of the disposal group.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupLifeAccidentandHealthPremiumsLifeOperations
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The Long-term care portion of life, accident and health premiums of the disposal group.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupLifeAccidentandHealthPremiumsLongTermCare
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents amount of other income attributable to the disposal group and the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as trading, available-for-sale, or held-to-maturity of the disposal group. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities of the disposal group.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupMarketableSecuritiesRealizedGainLossandOtherIncome
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, after investment expense, of income earned from investments in securities and real estate of the disposal group. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

No definition available.

+ Details

Name:	afg_DisposalGroupNetInvestmentIncome
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	afg_LifeAccidentandHealthBenefitsAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	afg_LifeAccidentandHealthNetEarnedPremiumsAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of operating expenses attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

+ Details

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of operating income or loss attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of other expense attributable to disposal group.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of sales or other form of revenues attributable to the disposal group, including a component of the entity (discontinued operation), during the reporting period.

+ References

+ Details

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