Investments - Debt Securities by Contractual Maturity Periods (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 1,133
Due after one year through five years	7,403
Due after five years through ten years	9,011
Due after ten years	4,212
Mortgage and other asset-backed securities	514
Amortized Cost	22,273	$ 21,909
Fair Value
Due in one year or less	1,143
Due after one year through five years	7,789
Due after five years through ten years	10,015
Due after ten years	5,211
Mortgage and other asset-backed securities	515
Fair Value	$ 24,673