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

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.

No definition available.

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