Investments - Schedule of sources of net investment income (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2020		Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Net Investment Income [Line Items]
Investment income		$ 474		$ 586	$ 1,023		$ 1,134
Equity in earnings of partnerships and similar investments		(54)		45	(29)		66
Investment expenses		(6)		(6)	(11)		(12)
Net Investment Income, Total		468	[1]	580	1,012	[1]	1,122
Fixed maturities
Net Investment Income [Line Items]
Investment income		485		478	976		947
Other
Net Investment Income [Line Items]
Investment income		18		34	46		59
Accounting Standards Update 2016-01 | Equity securities
Net Investment Income [Line Items]
Investment income	[2]	9	[1]	7	(3)	[1]	18
Investment income | Equity securities
Net Investment Income [Line Items]
Investment income		$ 16		$ 22	$ 33		$ 44

[1] Net investment income in the second quarter and first six months of 2020 includes income of less than $1 million and losses of $6 million, respectively, on investments held by the companies that comprise the Neon exited lines due primarily to the $7 million loss in first quarter of 2020 recorded on equity securities that are carried at fair value through net investment income.

[2] Although the change in the fair value of the majority of AFG’s equity securities is recorded in realized gains (losses) on securities, AFG records holding gains and losses in net investment income on equity securities classified as “trading” under previous guidance and on a small portfolio of limited partnership and similar investments that do not qualify for the equity method of accounting.