Contracts Accounted for as Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	$ 150	$ 106	$ 433	$ 505
Net expected loss to be expensed (present value)	250
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	132
Contra-paid, net	23
Salvage and subrogation recoverable, net	387
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(292)
Net expected loss to be expensed (present value)	$ 250