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Fair Value Measurements - Narrative (Details) | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2023 USD ($) | Dec. 31, 2024 USD ($) professional | Dec. 31, 2023 USD ($) | Dec. 31, 2021 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Goodwill, impairment loss | $ 26,000,000 |  |  |
AFG's internal investment professionals | professional |  | 20 |  |
Level 3 assets as a percentage of total assets measured at fair value |  | 7.00% |  |
Internally developed Level 3 assets |  | $ 932,000,000 |  |
Percentage of internally developed Level 3 assets compared to total Level 3 assets |  | 85.00% |  |
Percentage of Level 3 assets that were priced using a discounted cash flow approach |  | 69.00% |  |
Level 3 assets that were priced using a discounted cash flow approach |  | $ 647,000,000 |  |
Level 3 assets that were priced using unobservable internal models and third party inputs |  | $ 285,000,000 |  |
Percentage of level 3 assets that were priced using financial information from third parties |  | 11.00% |  |
Level 3 assets that were priced using financial information from third parties |  | $ 118,000,000 |  |
Percentage of level 3 assets that were priced using non-binding broker quotes or pricing services |  | 4.00% |  |
Level 3 assets that were priced using non-binding broker quotes or pricing services |  | $ 46,000,000 |  |
Contingent consideration - acquisitions |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Contingent consideration — acquisitions |  | $ 2,000,000 | $ 2,000,000 |
Verikai, Inc. |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Contingent consideration possible to be paid, maximum |  |  |  | $ 50,000,000
Verikai, Inc. | Contingent consideration - acquisitions |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Contingent consideration — acquisitions | 0 |  |  |
Gain on change in fair value of contingent consideration liability | $ 22,000,000 |  |  |

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