Fair Value Measurements - Narrative (Details)	6 Months Ended
	Jun. 30, 2023 USD ($) professional	Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFG's internal investment professionals | professional	20
Percentage of level three assets that were priced using a discounted cash flow approach	67.00%
Level three assets that were priced using a discounted cash flow approach	$ 462,000,000
Percentage of level three assets, equity securities, priced using broker quotes and internal models	18.00%
Level three assets, equity securities, priced using broker quotes and internal models	$ 123,000,000
Contingent consideration — acquisitions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of potential contingent consideration	25,000,000	$ 25,000,000
Change in fair value of contingent consideration liability	0
Contingent consideration — acquisitions | Verikai, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of potential contingent consideration	$ 23,000,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Level 3 assets as a percentage of total assets measured at fair value	7.00%
Percentage of level 3 assets that were priced using non-binding broker quotes	10.00%
Level 3 assets that were priced using non-binding broker quotes	$ 117,000,000
Percentage of level 3 assets that were priced by pricing services	3.00%
Level 3 assets that were priced by pricing services.	$ 37,000,000
Percentage of level 3 equity investments that do not qualify for equity accounting	27.00%
Level 3 assets that are equity securities that do not qualify for equity accounting	$ 316,000,000
Percentage of internally developed level 3 assets compared to total level 3 assets	60.00%
Internally developed level 3 assets	$ 690,000,000
Level 3 | Contingent consideration — acquisitions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of potential contingent consideration	$ 25,000,000	$ 25,000,000