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Contingencies (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract] |
Special charges to increase asbestos and environmental reserves | $ 30

X
- Definition Special charges to increase asbestos and environmental reserves. + References No definition available. + Details
Name: | afg_SpecialChargesToIncreaseAsbestosAndEnvironmentalReserves
Namespace Prefix: | afg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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