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Reinsurance and Indemnification - National Flood Insurance Program (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Sep. 30, 2025
Reinsurance Retention Policy [Line Items] |  |  |  |
Property-liability insurance premiums earned | $ 2,681 | $ 2,260 | $ 2,036 |
National Flood Insurance Program |  |  |  |
Reinsurance Retention Policy [Line Items] |  |  |  |
Legislation to reauthorize |  |  |  | $ 22,500
Reserve Fund borrowing capacity | 1,000 |  |  |
Reinsurance and indemnification recoverables, net | 22 | 279 |  |
Property-liability insurance premiums earned | 409 | 368 | 327 |
Ceded losses incurred | $ 111 | $ 618 | $ 102 |

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