Contracts Accounted for as Insurance - Reconciliation of Net Expected Loss to be Paid and Expensed (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	$ (737)	$ (1,183)	$ (1,303)
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(1,012)	$ (1,143)
Net expected loss to be expensed (present value)	439
Variable Interest Entity, Primary Beneficiary [Member]
Guarantor Obligations [Line Items]
Net expected loss to be expensed (present value)	33
Financial Guarantee Insurance And Other Product Line [Member]
Guarantor Obligations [Line Items]
Net expected loss to be paid (recovered) after recoveries for R&W	683
Contra-paid, net	51
Salvage and subrogation recoverable, net, and other recoverable	717
Loss and LAE reserve - financial guaranty insurance contracts, net of reinsurance	(1,012)
Net expected loss to be expensed (present value)	$ 439