Contracts Accounted for as Insurance - Loss and LAE Reserve and Salvage and Subrogation Recoverable Net of Reinsurance (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	$ 37	$ 79
Public finance | Financial Guarantee Insurance And Other Product Line | Consolidated Entity Excluding Variable Interest Entities (VIE)
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	72	61
Other structured finance | Financial Guarantee Insurance And Other Product Line | Consolidated Entity Excluding Variable Interest Entities (VIE)
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	42	42
Structured finance | Financial Guarantee Insurance And Other Product Line | Consolidated Entity Excluding Variable Interest Entities (VIE)
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	(35)	18
U.S. | Public finance | Financial Guarantee Insurance And Other Product Line | Consolidated Entity Excluding Variable Interest Entities (VIE)
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	71	60
U.S. | RMBS | Financial Guarantee Insurance And Other Product Line | Consolidated Entity Excluding Variable Interest Entities (VIE)
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	(77)	(24)
Non U.S. | Public finance | Financial Guarantee Insurance And Other Product Line | Consolidated Entity Excluding Variable Interest Entities (VIE)
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net reserve (salvage)	$ 1	$ 1