Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Unpaid Principal (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ liabilities with recourse	$ 51	$ 21
FG VIEs’ liabilities without recourse	16	15
Unpaid principal for FG VIEs’ liabilities with recourse	582	723
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ assets	266	265
Unpaid principal balance for FG VIEs’ assets that were 90 days or more past due	$ 29	$ 34