Contracts Accounted for as Insurance - Loss and LAE Reported on the Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Liability for Claims and Claims Adjustment Expense Including Salvage and Subrogation Recoverable [Line Items]
Loss and loss adjustment expenses (benefit)	$ (75)	$ (68)	$ (29)	$ (54)
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)	1	(23)	67	(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)	1	(23)	67	7
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	(9)
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)	(78)	(48)	(97)	(54)
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	3	1	2
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)	$ (76)	$ (45)	$ (96)	$ (52)