Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) professional
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	61.00%
Level three assets that were priced using a discounted cash flow approach	$ 361
Percentage of level three assets, equity securities, priced using broker quotes and internal models	28.00%
Level three assets, equity securities, priced using broker quotes and internal models	$ 168
Contingent consideration — acquisitions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of contingent consideration liability	$ 0
Level 3 | Continuing operations
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	6.00%
Percentage of level 3 assets that were priced using non-binding broker quotes	16.00%
Level 3 assets that were priced using non-binding broker quotes	$ 164
Level 3 assets that were priced by pricing services.	$ 58
Percentage of level 3 assets that were priced by pricing services	6.00%
Percentage of level 3 equity investments that do not qualify for equity accounting	19.00%
Level 3 assets that are equity securities that do not qualify for equity accounting	$ 186
Internally developed level 3 assets	$ 590
Percentage of internally developed level 3 assets compared to total level 3 assets	59.00%