Fair Value Measurements - Narrative (Details) $ in Millions	Jun. 30, 2021 USD ($) professional
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFG's internal investment professionals | professional	20
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	5.00%
Percentage of level 3 assets that were priced using non-binding broker quotes	24.00%
Level 3 assets that were priced using non-binding broker quotes	$ 206
Level three assets that were priced by pricing services.	$ 68
Percentage Of Level Three Assets That Were Priced By Pricing Services	8.00%
Internally developed level 3 assets	$ 491
Percentage Of Internally Developed Level Three Assets Compared to Total Level 3 Assets	57.00%