Contracts Accounted for as Insurance - Selected Information for Policies Paid In Installments (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Financial Guarantee Insurance Premiums [Line Items]
Premiums receivable, net of commission payable	$ 1,294	$ 1,286	$ 866	$ 904
Financial Guarantee Policies Paid in Installments [Member]
Financial Guarantee Insurance Premiums [Line Items]
Premiums receivable, net of commission payable	1,293	1,284
Gross deferred premium revenue	$ 1,679	$ 1,637
Weighted-average risk-free rate used to discount premiums	1.60%	1.70%
Weighted-average period of premiums receivable (in years)	12 years 8 months 12 days	13 years 3 months 18 days