Contracts Accounted for as Insurance - Selected Information for Policies Paid In Installments (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Financial Guarantee Insurance Premiums [Line Items]
Premiums receivable, net of commission payable	$ 1,321	$ 1,286	$ 844	$ 904
Financial Guarantee Policies Paid in Installments
Financial Guarantee Insurance Premiums [Line Items]
Premiums receivable, net of commission payable	1,320	1,284
Gross deferred premium revenue	$ 1,668	$ 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