Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Variable Interest Entity [Line Items]
Assets	$ 11,944	$ 16,843
Liabilities	6,643	11,551
Cash	108	107	$ 131
Variable Interest Entity, Primary Beneficiary | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	531	702
Variable Interest Entity, Primary Beneficiary | Nonrecourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	11	13
Variable Interest Entity, Primary Beneficiary | Puerto Rico Trusts | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	347	495
Variable Interest Entity, Primary Beneficiary | Underlying, Other | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	8	7
Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	156	176
Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien | Nonrecourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	11	13
Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	20	24
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	327	416
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | Puerto Rico Trusts
Variable Interest Entity [Line Items]
Assets	147	212
Total assets carried at fair value	146	209
Cash		2
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | Underlying, Other
Variable Interest Entity [Line Items]
Assets	7	7
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien
Variable Interest Entity [Line Items]
Assets	146	167
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien
Variable Interest Entity [Line Items]
Assets	$ 27	$ 30