Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Summary of Carrying value of long-term debt
Long-term debt	$ 949	$ 953
Notes payable secured by real estate due 2013 through 2016	62	62
Secured borrowings ($15 and $16 guaranteed by AFG)	15	19
AFG [Member]
Summary of Carrying value of long-term debt
Other long-term debt	3	3
Long-term debt	840	840
Subsidiaries [Member]
Summary of Carrying value of long-term debt
Long-term debt	89	93
Notes payable secured by real estate due 2013 through 2016	62	62
Secured borrowings ($15 and $16 guaranteed by AFG)	15	19
National Interstate bank credit facility	12	12
9-7/8% Senior Notes due June 2019 [Member] | AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	350	350
6-3/8% Senior Notes due June 2042 [Member] | AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	230	230
5-3/4% Senior Notes due August 2042 [Member] | AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	125	125
7% Senior Notes due September 2050 [Member] | AFG [Member]
Summary of Carrying value of long-term debt
Senior Notes	132	132
Payable To Subsidiary Trusts [Member]
Summary of Carrying value of long-term debt
AAG Holding Variable Rate Subordinated Debentures due May 2033	$ 20	$ 20