Managed Investment Entities - Selected financial information related to CLOs (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Gains (losses) on change in fair value of assets/liabilities:
Assets	[1]	$ (29)	$ (9)	$ (15)	$ (4)
Liabilities	[1]	27	20	10	15
Management fees paid to AFG		4	5	8	9
CLO earnings (losses) attributable to AFG shareholders	[2]	4	5	7	11
Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Investment in CLO tranches at end of period		$ 192	$ 188	$ 192	$ 188	$ 215

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

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