Contracts Accounted for as Insurance - Loss and LAE Reported on the Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and loss adjustment expenses (benefit)	$ 55	$ (11)	$ 59	$ 46
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)	56	11	52	66
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)	56	11	52	66
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)	0	0	0	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)	(2)	(22)	4	(19)
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)	1	0	3	(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)	$ (1)	$ (22)	$ 7	$ (20)