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

The sum of amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2 for each applicable quarter end period.

No definition available.

Name:	afg_FairValueAssetsLevel1toLevel2TransfersDuringthePeriodAmount
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The sum of amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1 for each applicable quarter end period.

No definition available.

Name:	afg_FairValueAssetsLevel2toLevel1TransfersDuringthePeriodAmount
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Risk associated with risk of surrenders, expressed as a percentage, used as an input to measure fair value.

No definition available.

Name:	afg_FairValueInputsSurrenders
Namespace Prefix:	afg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Fair value measurement with unobservable inputs reconciliation recurring basis liability gain (loss) included in earnings on liabilities still outstanding.

No definition available.

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

Fair Value Measurements.

No definition available.

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

Level Three Asset As Percentage Of Asset Measured At Fair Value.

No definition available.

Name:	afg_LevelThreeAssetAsPercentageOfAssetMeasuredAtFairValue
Namespace Prefix:	afg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Level three assets that were priced using non-binding broker quotes.

No definition available.

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

Financial liabilities on annuities in the payout phase that are contingent on the survival of the annuitant(s).

No definition available.

Name:	afg_LifeContingentAnnuities
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Number of internal investment professionals.

No definition available.

Name:	afg_NumberOfInternalInvestmentProfessionals
Namespace Prefix:	afg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The sum of number of stocks transferred from Level 1 to Level 2 for each applicable quarter end period.

No definition available.

Name:	afg_NumberofStocksTransferredfromLevel1toLevel2DuringthePeriod
Namespace Prefix:	afg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The sum of number of stocks transferred from Level 2 to Level 1 for each applicable quarter end period.

No definition available.

Name:	afg_NumberofStocksTransferredfromLevel2toLevel1DuringthePeriod
Namespace Prefix:	afg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Percentage of Internally Developed Level 3 Assets to Total Shareholders' Equity

No definition available.

Name:	afg_PercentageOfInternallyDevelopedLevelThreeAssetsToShareholdersEquity
Namespace Prefix:	afg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of Internally Developed Level Three Assets to Total Assets.

No definition available.

Name:	afg_PercentageOfInternallyDevelopedLevelThreeAssetsToTotalAssets
Namespace Prefix:	afg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of level 3 assets that were priced using non-binding broker quotes.

No definition available.

Name:	afg_PercentageOfLevelThreeAssetsThatWerePricedUsingNonBindingBrokerQuotes
Namespace Prefix:	afg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Name:	us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

Name:	us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=afg_FixedIndexedAnnuitiesEmbeddedDerivativeMajorityofFutureYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=afg_FixedIndexedAnnuitiesEmbeddedDerivativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_PreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_MandatorilyRedeemablePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: