Fair Value Measurements - Narrative (Details) $ in Millions	Mar. 31, 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	8.00%
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	$ 109
Percentage of level 3 assets that were priced by pricing services	1.00%
Level 3 assets that were priced by pricing services.	$ 10
Percentage of level 3 equity investments that do not qualify for equity accounting	31.00%
Level 3 assets that are equity securities that do not qualify for equity accounting	$ 397
Percentage of internally developed level 3 assets compared to total level 3 assets	60.00%
Internally developed level 3 assets	$ 781
Percentage of level three assets that were priced using a discounted cash flow approach	73.00%
Level three assets that were priced using a discounted cash flow approach	$ 566
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	$ 144