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Contracts Accounted for as Financial Guaranty Insurance - Loss and LAE Reserve and Salvage and Subrogation Recoverable Net of Reinsurance (Details) - USD ($) $ in Millions | Mar. 31, 2026 | Dec. 31, 2025
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Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | $ (124) | $ (139)
Public finance | Financial Guarantee Insurance And Other Product Line |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | (40) | (48)
Other structured finance | Financial Guarantee Insurance And Other Product Line |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | 59 | 59
Structured finance | Financial Guarantee Insurance And Other Product Line |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | (84) | (91)
United States | Public finance | Financial Guarantee Insurance And Other Product Line |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | (64) | (66)
United States | RMBS | Financial Guarantee Insurance And Other Product Line |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | (143) | (150)
Non-U.S. public finance | Public finance | Financial Guarantee Insurance And Other Product Line |  |
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Net Reserve (Recoverable) | $ 24 | $ 18

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- Definition [Line Items] for Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Table] + References No definition available. + Details
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- Definition Represents the reserve for losses and loss adjustment expenses, net of reinsurance recoverable on unpaid losses and net of salvage and subrogation recoverable. + References No definition available. + Details
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