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Contingencies - Narrative (Details) - Run-off Long-term Care and Life $ in Millions | Dec. 24, 2015 USD ($)
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Loss Contingencies [Line Items] |
Contingent capital support agreement amount | $ 35
Contingent capital support agreement contractual term | 5 years

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- Definition Amount relating to the capital maintenance agreement entered in connection with obtaining regulatory approval for the sale of substantially all of the disposal group. This amount is available on an as-needed basis to maintain specified surplus levels and is subject to immediate reimbursement by the counterparty. + References No definition available. + Details
Name: | afg_DisposalGroupContingentCapitalSupportAgreementAmount
Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Contractual term relating to the capital maintenance agreement entered in connection with obtaining regulatory approval for the sale of substantially all of the disposal group. + References No definition available. + Details
Name: | afg_DisposalGroupContingentCapitalSupportAgreementContractualTerm
Namespace Prefix: | afg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=afg_RunOffLongTermCareAndLifeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |