Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Net Amortized Cost
Less than one year	$ 1,198
One year through five years	5,619
After five years through ten years	3,160
Greater than ten years	3,897
Net Amortized Cost	17,108	$ 15,898
Fair Value
Less than one year	1,214
One year through five years	5,925
After five years through ten years	3,448
Greater than ten years	4,620
Total	18,554	16,922
Residential mortgage-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	666
Net Amortized Cost	666	508
Fair Value
Debt securities, maturity, without single maturity date	702
Total	702	533
Commercial mortgage-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	754
Net Amortized Cost	754	654
Fair Value
Debt securities, maturity, without single maturity date	823
Total	823	700
Other asset-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	1,814
Net Amortized Cost	1,814	1,397
Fair Value
Debt securities, maturity, without single maturity date	1,822
Total	$ 1,822	$ 1,405