Fair Value Measurements - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 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	62.00%
Level three assets that were priced using a discounted cash flow approach	$ 373
Percentage of level three assets, equity securities, priced using broker quotes and internal models	27.00%
Level three assets, equity securities, priced using broker quotes and internal models	$ 161
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	15.00%
Level 3 assets that were priced using non-binding broker quotes	$ 148
Level 3 assets that were priced by pricing services.	$ 23
Percentage of level 3 assets that were priced by pricing services	2.00%
Percentage of level 3 equity investments that do not qualify for equity accounting	22.00%
Level 3 assets that are equity securities that do not qualify for equity accounting	$ 213
Internally developed level 3 assets	$ 599
Percentage of internally developed level 3 assets compared to total level 3 assets	61.00%