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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
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Mar. 31, 2025 | Mar. 31, 2024
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items] |  |
Loss and loss adjustment expenses (benefit) | $ 40 | $ (1)
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) | 42 | (2)
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) | 36 | (2)
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) | 6 | 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) | 0 | 2
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)
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

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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 Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(5)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 + Details
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