Condensed Consolidating Information (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues:
Property and casualty insurance premiums									$ 2,759	$ 2,550	$ 2,412
Life, accident and health premiums									430	451	444
Realized gains (losses)									73	88	38
Income of managed investment entities									72	23
Investment and other income									1,416	1,385	1,426
Total revenues	1,283	1,335	1,093	1,039	1,156	1,255	1,052	1,034	4,750	4,497	4,320
Costs and Expenses:
Insurance benefits and expenses									3,671	3,297	2,978
Interest charges on borrowed money									85	78	67
Expenses of managed investment entities									71	55
Other operating and general expenses									363	378	463
Total costs and expenses									4,190	3,808	3,508
Operating earnings before income taxes									560	689	812
Provision (credit) for income taxes									240	266	282
Net earnings, including noncontrolling interests	127	107	37	49	109	126	100	88	320	423	530
Less: Net earnings (loss) attributable to noncontrolling interests									(23)	(56)	11
Net Earnings Attributable to Shareholders	109	96	55	83	133	132	108	106	343	479	519
AFG [Member]
Revenues:
Investment and other income									2	4	2
Equity in earnings of subsidiaries									710	850	896
Total revenues									712	854	898
Costs and Expenses:
Interest charges on borrowed money									64	58	50
Other operating and general expenses									65	51	47
Total costs and expenses									129	109	97
Operating earnings before income taxes									583	745	801
Provision (credit) for income taxes									240	266	282
Net earnings, including noncontrolling interests									343	479	519
Net Earnings Attributable to Shareholders									343	479	519
GAFRI [Member]
Revenues:
Realized gains (losses)									(1)	(2)	(7)
Investment and other income									11	11	10
Equity in earnings of subsidiaries									189	195	73
Total revenues									199	204	76
Costs and Expenses:
Other operating and general expenses									15	16	20
Total costs and expenses									15	16	20
Operating earnings before income taxes									184	188	56
Provision (credit) for income taxes									62	72	17
Net earnings, including noncontrolling interests									122	116	39
Net Earnings Attributable to Shareholders									122	116	39
AAG Holding [Member]
Revenues:
Equity in earnings of subsidiaries									216	242	115
Total revenues									216	242	115
Costs and Expenses:
Interest charges on borrowed money									25	25	25
Other operating and general expenses									5	5	6
Total costs and expenses									30	30	31
Operating earnings before income taxes									186	212	84
Provision (credit) for income taxes									64	72	26
Net earnings, including noncontrolling interests									122	140	58
Net Earnings Attributable to Shareholders									122	140	58
All Other Subs [Member]
Revenues:
Property and casualty insurance premiums									2,759	2,550	2,412
Life, accident and health premiums									430	451	444
Realized gains (losses)									75	90	44
Income of managed investment entities									72	23
Investment and other income									1,430	1,392	1,437
Total revenues									4,766	4,506	4,337
Costs and Expenses:
Insurance benefits and expenses									3,671	3,297	2,978
Interest charges on borrowed money									16	17	15
Expenses of managed investment entities									71	55
Other operating and general expenses									284	306	391
Total costs and expenses									4,042	3,675	3,384
Operating earnings before income taxes									724	831	953
Provision (credit) for income taxes									283	314	327
Net earnings, including noncontrolling interests									441	517	626
Less: Net earnings (loss) attributable to noncontrolling interests									(23)	(56)	11
Net Earnings Attributable to Shareholders									464	573	615
Consol. Entries [Member]
Revenues:
Realized gains (losses)									(1)		1
Investment and other income									(27)	(22)	(23)
Equity in earnings of subsidiaries									(1,115)	(1,287)	(1,084)
Total revenues									(1,143)	(1,309)	(1,106)
Costs and Expenses:
Interest charges on borrowed money									(20)	(22)	(23)
Other operating and general expenses									(6)		(1)
Total costs and expenses									(26)	(22)	(24)
Operating earnings before income taxes									(1,117)	(1,287)	(1,082)
Provision (credit) for income taxes									(409)	(458)	(370)
Net earnings, including noncontrolling interests									(708)	(829)	(712)
Net Earnings Attributable to Shareholders									$ (708)	$ (829)	$ (712)