Investments Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investment grade fixed income securities
Schedule of Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net (1) (2)	$ (579)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(137)
Total unrealized losses	(716)	$ (61)
Below investment grade fixed income securities
Schedule of Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net (1) (2)	(311)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(257)
Total unrealized losses	(568)	(35)
Unrealized losses having loss of less than twenty percent, less than 12 months	(304)
Fixed income securities
Schedule of Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net (1) (2)	(890)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(394)
Total unrealized losses	$ (1,284)	$ (96)