Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Variable Interest Entity [Line Items]
Assets	$ 12,291	$ 12,539
Liabilities	6,509	6,774
Cash	147	97	$ 108
Variable Interest Entity, Primary Beneficiary | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	382	543
Variable Interest Entity, Primary Beneficiary | Nonrecourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	10	11
Variable Interest Entity, Primary Beneficiary | Puerto Rico Trusts | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	218	366
Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	144	156
Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien | Nonrecourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	10	11
Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien | Recourse | Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
Liabilities	20	21
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	156	328
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | Puerto Rico Trusts
Variable Interest Entity [Line Items]
Assets	2	155
Total assets carried at fair value	2	1
Cash		154
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien
Variable Interest Entity [Line Items]
Assets	129	145
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien
Variable Interest Entity [Line Items]
Assets	$ 25	$ 28