Contracts Accounted for as Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	$ 433	$ 505	$ 517	$ 522
Net expected loss to be expensed (present value)	203
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	188
Contra-paid, net	22
Salvage and subrogation recoverable, net	294
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(301)
Net expected loss to be expensed (present value)	$ 203