Contracts Accounted for as Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	$ 106	$ 505	$ 522	$ 411
Net expected loss to be expensed (present value)	240
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	89
Contra-paid, net	23
Salvage and subrogation recoverable, net	393
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(265)
Net expected loss to be expensed (present value)	$ 240