Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total premiums earned										$ 4,328	$ 4,224	$ 3,878
Net investment income										1,696	1,633	1,501
Other income										224	243	122
Revenues before realized gains (losses)										6,477	6,325	5,681
Realized gains (losses) on securities										19	(19)	52
Realized gains (losses) on subsidiaries										2	(161)	0
Total revenues		$ 1,737	$ 1,705	$ 1,581	$ 1,475	$ 1,618	$ 1,687	$ 1,543	$ 1,297	6,498	6,145	5,733
Property and casualty insurance
Segment Reporting Information [Line Items]
Net investment income										350	319	294
Other income	[1]									51	78	9
Revenues before realized gains (losses)										4,729	4,621	4,181
Annuity
Segment Reporting Information [Line Items]
Net investment income										1,356	1,224	1,136
Other income										103	98	97
Revenues before realized gains (losses)										1,459	1,322	1,233
Run-off long-term care and life
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)	[2]									49	188	195
Other
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)										240	194	72
Property and transportation
Segment Reporting Information [Line Items]
Total premiums earned										1,662	1,599	1,544
Specialty casualty
Segment Reporting Information [Line Items]
Total premiums earned										2,006	2,011	1,765
Specialty financial
Segment Reporting Information [Line Items]
Total premiums earned										557	517	469
Other specialty
Segment Reporting Information [Line Items]
Total premiums earned										$ 103	$ 97	$ 100

[1] Includes pretax income of $32 million (before noncontrolling interest) from the sale of an apartment property in the second quarter of 2016, $51 million (before noncontrolling interest) from the sale of a hotel in the second quarter of 2015 and $15 million from the sale of an apartment property in the fourth quarter of 2015.

[2] AFG sold substantially all of its run-off long-term care insurance business in December 2015.