Investments - Schedule of sources of net investment income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020		Mar. 31, 2019
Net Investment Income [Line Items]
Investment income		$ 549		$ 548
Investment expenses		(5)		(6)
Net investment income (b)		544	[1]	542
Fixed maturities
Net Investment Income [Line Items]
Investment income		491		469
Equity in earnings of partnerships and similar investments
Net Investment Income [Line Items]
Investment income		25		21
Other
Net Investment Income [Line Items]
Investment income		28		25
Accounting Standards Update 2016-01 | Equity securities
Net Investment Income [Line Items]
Investment income	[2]	(12)	[1]	11
Investment income | Equity securities
Net Investment Income [Line Items]
Investment income		$ 17		$ 22

[1] Net investment income in the first three months of 2020 includes a loss of $6 million on investments held by the companies that comprise the Neon exited lines due primarily to the $7 million loss 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.