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Contracts Accounted for as Insurance - Loss and LAE Reported on the Statements of Operations (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | $ (30) | $ (51) | $ 38 | $ (54)
Public finance | Financial Guarantee Insurance And Other Product Line |  |  |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | (7) | (11) | 64 | (12)
Public finance | Financial Guarantee Insurance And Other Product Line | United States |  |  |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | (5) | (11) | 46 | (12)
Public finance | Financial Guarantee Insurance And Other Product Line | Non United States |  |  |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | (2) | 0 | 18 | 0
RMBS | Financial Guarantee Insurance And Other Product Line | United States |  |  |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | (25) | (39) | (25) | (42)
Other structured finance | Financial Guarantee Insurance And Other Product Line |  |  |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | 2 | (1) | (1) | 0
Structured finance | Financial Guarantee Insurance And Other Product Line |  |  |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |  |  |
Loss and loss adjustment expenses (benefit) | $ (23) | $ (40) | $ (26) | $ (42)

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