Investments - Debt Securities by Contractual Maturity Periods (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 1,020
Due after one year through five years	7,046
Due after five years through ten years	8,970
Due after ten years	4,144
Mortgage and other asset-backed securities	495
Amortized Cost	21,675	$ 21,909
Fair Value
Due in one year or less	1,023
Due after one year through five years	7,104
Due after five years through ten years	9,109
Due after ten years	4,849
Mortgage and other asset-backed securities	488
Fair Value	$ 22,573