Managed Investment Entities - Selected financial information related to CLOs (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Gains (losses) on change in fair value of assets/liabilities:
Assets	[1]	$ 20	$ (8)	$ 5	$ (12)
Liabilities	[1]	(25)	9	(15)	24
Management fees paid to AFG		4	5	12	14
CLO earnings (losses) attributable to AFG shareholders	[2]	4	5	11	16
Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Investment in CLO tranches at end of period		$ 191	$ 261	$ 191	$ 261	$ 215

[1] Included in revenues in AFG’s Statement of Earnings.

[2] Included in earnings before income taxes in AFG’s Statement of Earnings.