Contracts Accounted for as Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	$ 490	$ 560	$ 522	$ 727	$ 442	$ 411
Net expected loss to be expensed	196
Financial Guarantee Insurance And Other Product Line
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) - financial guaranty insurance	249
Contra-paid, net	21
Salvage and subrogation recoverable, net	281
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(355)
Net expected loss to be expensed	$ 196