Fair Value Measurements - Narrative (Details) $ in Millions	Jun. 30, 2024 USD ($) professional
Fair Value Disclosures [Abstract]
AFG's internal investment professionals | professional	20
Level 3 assets as a percentage of total assets measured at fair value	9.00%
Percentage of level 3 assets that were priced using non-binding broker quotes	8.00%
Level 3 assets that were priced using non-binding broker quotes	$ 119
Percentage of level 3 assets that were priced by pricing services	1.00%
Level 3 assets that were priced by pricing services.	$ 8
Percentage of level 3 equity investments that do not qualify for equity accounting	32.00%
Level 3 assets that are equity securities that do not qualify for equity accounting	$ 440
Percentage of internally developed level 3 assets compared to total level 3 assets	59.00%
Internally developed level 3 assets	$ 815
Percentage of level three assets that were priced using a discounted cash flow approach	71.00%
Level three assets that were priced using a discounted cash flow approach	$ 577
Percentage of level three assets, equity securities, priced using broker quotes and internal models	20.00%
Level three assets, equity securities, priced using broker quotes and internal models	$ 159