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

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

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

No definition available.

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

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

No definition available.

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

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

No definition available.

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

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

No definition available.

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

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.

No definition available.

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

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.

No definition available.

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

Life, accident and health benefits.

No definition available.

Name:	afg_LifeAccidentandHealthBenefitsAbstract
Namespace Prefix:	afg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Life, accident and health net earned premiums.

No definition available.

Name:	afg_LifeAccidentandHealthNetEarnedPremiumsAbstract
Namespace Prefix:	afg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of operating expense attributable to disposal group, including, but not limited to, discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721673-107760

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

Amount of operating income (loss) attributable to disposal group, including, but not limited to, discontinued operation.

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

Amount of other expense attributable to disposal group, including, but not limited to, discontinued operation.

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

Amount of revenue attributable to disposal group, including, but not limited to, discontinued operation.