Quarterly Operating Results (Unaudited) - Narrative (Details) - USD ($) $ in Millions			3 Months Ended							12 Months Ended
		Dec. 24, 2015	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Operating Results (Unaudited) [Line Items]
Realized gains (losses) on subsidiaries										$ 2	$ (161)	$ 0
Other income										224	243	122
Income tax expense (benefit)										119	195	220
Run-off long-term care insurance business
Quarterly Operating Results (Unaudited) [Line Items]
Realized gains (losses) on subsidiaries		$ (166)			$ 2	$ (4)			$ (162)		(166)
Property and casualty insurance
Quarterly Operating Results (Unaudited) [Line Items]
Other income	[1]									51	78	9
Property and casualty insurance | Other lines
Quarterly Operating Results (Unaudited) [Line Items]
Special charges related to the exit of certain lines of business within subsidiaries					65
Special charges to increase asbestos and environmental reserves				$ 36			$ 67			36	67	24
Property and casualty insurance | Other lines | Increased insurance loss reserves related to medical malpractice and general liability lines
Quarterly Operating Results (Unaudited) [Line Items]
Special charges related to the exit of certain lines of business within subsidiaries					57
Property and casualty insurance | Real estate investment
Quarterly Operating Results (Unaudited) [Line Items]
Other income					$ 32	$ 15		$ 51
Other
Quarterly Operating Results (Unaudited) [Line Items]
Special charges to increase asbestos and environmental reserves										5	12	6
Other | Former railroad and manufacturing operations
Quarterly Operating Results (Unaudited) [Line Items]
Special charges to increase asbestos and environmental reserves				$ 5			$ 12
AFG
Quarterly Operating Results (Unaudited) [Line Items]
Income tax expense (benefit)			$ (177)							$ 119	$ 195	$ 220

[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.