Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Net Amortized Cost
Less than one year	$ 1,219
One year through five years	5,292
After five years through ten years	3,135
Greater than ten years	3,708
Net Amortized Cost	16,097	$ 15,898
Fair Value
Less than one year	1,225
One year through five years	5,399
After five years through ten years	3,233
Greater than ten years	4,110
Total	16,717	16,922
Residential mortgage-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	574
Net Amortized Cost	574	508
Fair Value
Debt securities, maturity, without single maturity date	612
Total	612	533
Commercial mortgage-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	662
Net Amortized Cost	662	654
Fair Value
Debt securities, maturity, without single maturity date	704
Total	704	700
Other asset-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	1,507
Net Amortized Cost	1,507	1,397
Fair Value
Debt securities, maturity, without single maturity date	1,434
Total	$ 1,434	$ 1,405