Contracts Accounted for as Insurance - Selected Information for Policies Paid In Installments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financial Guarantee Insurance Premiums [Line Items]
Premiums receivable, net of commission payable	$ 1,286	$ 904	$ 915	$ 576
Financial Guarantee Policies Paid in Installments [Member]
Financial Guarantee Insurance Premiums [Line Items]
Premiums receivable, net of commission payable	1,284	903
Gross deferred premium revenue	$ 1,637	$ 1,313
Weighted-average risk-free rate used to discount premiums (as a percent)	1.70%	2.30%
Weighted-average period of premiums receivable (in years)	13 years 3 months 18 days	9 years 1 month 6 days