Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes		$ 210	$ 41	$ 706	$ 458
Realized gains (losses) on securities		34	(12)	(28)	(1)
Earnings before income taxes		244	29	678	457
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		38	(81)	201	69
Investment and other income, net	[1]	101	87	300	271
Earnings before realized gains (losses) and income taxes		139	6	501	340
Annuity
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes		117	102	341	283
Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	[2]	(46)	(67)	(136)	(165)
Specialty Property and transportation | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		0	6	56	70
Specialty casualty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		49	2	119	46
Specialty financial | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		9	(3)	46	42
Other specialty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting		(3)	4	(1)	3
Other lines | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	[3]	$ (17)	$ (90)	$ (19)	$ (92)

[1] Includes income of $13 million (before noncontrolling interest) from the sale of a hotel in the first quarter of 2017.

[2] Includes holding company interest and expenses, including losses on retirement of debt of $4 million in the third quarter of 2017 and $7 million in the second quarter of 2017, and special charges of $9 million and $24 million in the third quarter of 2018 and 2017, respectively, to increase A&E reserves related to AFG’s former railroad and manufacturing operations.

[3] Includes special charges of $18 million and $89 million in the third quarter of 2018 and 2017, respectively, to increase asbestos and environmental (“A&E”) reserves.