Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Net Amortized Cost
Less than one year	$ 1,588
One year through five years	6,009
After five years through ten years	3,466
Greater than ten years	3,947
Net Amortized Cost	18,859	$ 15,898
Fair Value
Less than one year	1,604
One year through five years	6,329
After five years through ten years	3,774
Greater than ten years	4,704
Total	20,398	16,922
Residential mortgage-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	680
Net Amortized Cost	680	508
Fair Value
Debt securities, maturity, without single maturity date	713
Total	713	533
Commercial mortgage-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	930
Net Amortized Cost	930	654
Fair Value
Debt securities, maturity, without single maturity date	1,012
Total	1,012	700
Other asset-backed securities
Net Amortized Cost
Debt securities, maturity, without single maturity date	2,239
Net Amortized Cost	2,239	1,397
Fair Value
Debt securities, maturity, without single maturity date	2,262
Total	$ 2,262	$ 1,405