Financial Guaranty Variable Interest Entities and Consolidated Investment Vehicles - Unpaid Principal (Details) - Variable Interest Entity, Primary Beneficiary - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ liabilities with recourse	$ 31	$ 25
FG VIEs’ liabilities without recourse	16	16
Unpaid principal for FG VIEs’ liabilities with recourse	420	568
Financial Guaranty Variable Interest Entities
Variable Interest Entity [Line Items]
FG VIEs’ assets	260	259
Unpaid principal balance for FG VIEs’ assets that were 90 days or more past due	$ 27	$ 29