Fair Value Measurements - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) professional
Fair Value Measurements (Textual) [Abstract]
AFG's internal investment professionals | professional	20
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	$ 142
Level 3 assets that were priced by pricing services.	$ 55
Percentage of Level 3 assets that were priced by pricing services	6.00%
Percentage of Level 3 assets that were priced using a discounted cash flow approach	55.00%
Level 3 assets that were priced using a discounted cash flow approach	$ 307
Percentage of equity securities in Level 3 priced using broker quotes and internal models	26.00%
Equity securities in Level 3 priced using broker quotes and internal models	$ 144
Level 3
Fair Value Measurements (Textual) [Abstract]
Internally developed Level 3 assets	$ 557
Percentage of internally developed Level 3 assets compared to total Level 3 assets	60.00%
Level 3 | Continuing operations
Fair Value Measurements (Textual) [Abstract]
Percentage of equity investments in Level 3 assets that do not qualify for equity accounting	18.00%
Equity investments in Level 3 assets that do not qualify for equity accounting	$ 166