Managed Investment Entities - Selected financial information related to CLOs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Gains (losses) on change in fair value of assets/liabilities:
Assets	$ 21	$ 363	$ 67	$ (316)
Liabilities	(15)	(366)	(59)	300
Management fees paid to AFG	4	4	8	8
CLO earnings (losses) attributable to AFG shareholders	14	2	32	(34)
Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Investment in CLO tranches	57	157	57	157	$ 200
Variable interest entity, primary beneficiary | Continuing operations
Variable Interest Entity [Line Items]
Investment in CLO tranches	57	39	57	39
Gains (losses) on change in fair value of assets/liabilities:
CLO earnings (losses) attributable to AFG shareholders	7	0	12	(11)
Variable interest entity, primary beneficiary | Net earnings (loss) from discontinued operations | Annuity subsidiaries
Variable Interest Entity [Line Items]
Investment in CLO tranches	0	118	0	118
Gains (losses) on change in fair value of assets/liabilities:
CLO earnings (losses) attributable to AFG shareholders	$ 7	$ 2	$ 20	$ (23)