Investments Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Total unrealized losses	$ (1)
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)	(66)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(17)
Total unrealized losses	(83)	$ (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)	(70)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(64)
Total unrealized losses	(134)	(35)
Unrealized losses having loss of less than twenty percent, less than 12 months	(53)
Fixed income securities
Schedule of Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net (1) (2)	(136)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(81)
Total unrealized losses	$ (217)	$ (96)