Investments Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Investment grade fixed income securities
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost (1) (2)	$ (23,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(13,000,000)
Total unrealized losses	(36,000,000)	$ (691,000,000)
Below investment grade fixed income securities
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost (1) (2)	(46,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(4,000,000)
Total unrealized losses	(50,000,000)	(266,000,000)
Unrealized losses having loss of less than twenty percent, less than 12 months	25,000,000
Unrealized losses having loss of less than twenty percent, more than 12 months	0
Fixed income securities
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost (1) (2)	(69,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(17,000,000)
Total unrealized losses	$ (86,000,000)	$ (957,000,000)