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Segments of Operations (Details Textual) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 segment | Mar. 31, 2014
Segment Reporting Information [Line Items] |  |
Number of segments | 4 us-gaap_NumberOfReportableSegments |
Maximum [Member] | Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Earnings (losses) of managed investment entities attributable to noncontrolling interests (are less than in 2014) |  | $ 1 afg_EarningsLossesOfVariableInterestEntitiesAttributableToNoncontrollingInterests / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_CorporateAndOtherMember

X
- Definition Earnings (losses) of variable interest entities attributable to noncontrolling interests. + References No definition available. + Details
Name: | afg_EarningsLossesOfVariableInterestEntitiesAttributableToNoncontrollingInterests
Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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