Investments - Schedule of sources of net investment income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Net Investment Income [Line Items]
Investment income		$ 548	$ 500
Investment expenses		(6)	(5)
Net investment income		542	495
Fixed maturities
Net Investment Income [Line Items]
Investment income		469	412
Equity in earnings of partnerships and similar investments
Net Investment Income [Line Items]
Investment income		21	46
Other
Net Investment Income [Line Items]
Investment income		25	23
Accounting Standards Update 2016-01 | Equity securities
Net Investment Income [Line Items]
Investment income	[1]	11	(1)
Investment income | Equity securities
Net Investment Income [Line Items]
Investment income		$ 22	$ 20

[1] 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.