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Property Casualty Loss and Loss Expenses - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Reserve for loss and loss expenses | $ 11,260 |  | $ 11,260 |  | $ 10,003
Prior accident years | (22) | $ (71) | (176) | $ (211) |
Life Insurance Segment |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Reserve for loss and loss expenses | 65 | 62 | 65 | 62 |
Commercial Insurance |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | (18) | (50) | (103) | (117) |
Commercial Insurance | Commercial Property Line |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | (38) | (33) | (113) | (76) |
Commercial Insurance | Workers' Compensation Line |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | (17) | (16) | (45) | (56) |
Commercial Insurance | Commercial Casualty Line |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | 24 |  | 21 | 27 |
Commercial Insurance | Commercial Auto Line |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | 10 |  | 35 | (10) |
Personal Insurance |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | 14 | 1 | (24) | (27) |
Personal Insurance | Homeowner |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years |  |  | (47) | (37) |
Excess and Surplus Lines Insurance |  |  |  |  |
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters |  |  |  |  |
Prior accident years | $ (4) | $ 5 | $ (18) | $ 5 |

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