Contracts Accounted for as Insurance - Loss and LAE Reserve and Salvage and Subrogation Recoverable Net of Reinsurance (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Net Reserve (Recoverable)	$ 10	$ 75
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)	101	120
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)	36	42
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)	(91)	(45)
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)	100	119
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)	(127)	(87)
Non 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)	$ 1	$ 1