Variable Interest Entities - Consolidated FG VIE's By Type of Collateral (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 17,614	$ 15,334
Liabilities	11,218	8,629
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	271	296
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | Recourse
Variable Interest Entity [Line Items]
Liabilities	281	316
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | Nonrecourse
Variable Interest Entity [Line Items]
Liabilities	20	17
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien
Variable Interest Entity [Line Items]
Assets	227	243
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien | Recourse
Variable Interest Entity [Line Items]
Liabilities	235	260
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | First Lien | Nonrecourse
Variable Interest Entity [Line Items]
Liabilities	20	17
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien
Variable Interest Entity [Line Items]
Assets	44	53
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien | Recourse
Variable Interest Entity [Line Items]
Liabilities	46	56
Financial Guaranty Variable Interest Entities | Variable Interest Entity, Primary Beneficiary | United States | RMBS | Second Lien | Nonrecourse
Variable Interest Entity [Line Items]
Liabilities	$ 0	$ 0