Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Unpaid Principal (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ liabilities with recourse	$ 36	$ 38
FG VIEs’ liabilities without recourse	16	16
Unpaid principal for FG VIEs’ liabilities with recourse	189	193
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ assets	262	264
Unpaid principal balance for FG VIEs’ assets that were 90 days or more past due	$ 27	$ 27