Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Unpaid Principal (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ liabilities with recourse	$ 29	$ 25
FG VIEs’ liabilities without recourse	16	16
Unpaid principal for FG VIEs’ liabilities with recourse	411	568
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ assets	261	259
Unpaid principal balance for FG VIEs’ assets that were 90 days or more past due	$ 25	$ 29