Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost (1) (2)	$ (22,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost (3) (4)	(19,000,000)
Total unrealized losses	(41,000,000)
Available for sale securities, unrealized losses having loss of twenty percent or higher, greater than 12 months	0
Investment grade
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost (1) (2)	(7,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost (3) (4)	(13,000,000)
Total unrealized losses	(20,000,000)	$ (268,000,000)
Below investment grade
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost (1) (2)	(15,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost (3) (4)	(6,000,000)
Total unrealized losses	(21,000,000)	$ (121,000,000)
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	$ (6,000,000)