Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Investment grade
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	$ (48,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(13,000,000)
Total unrealized losses	(61,000,000)	$ (691,000,000)
Below investment grade
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(27,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(8,000,000)
Total unrealized losses	(35,000,000)	(266,000,000)
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	14,000,000
Unrealized losses related to securities with unrealized loss position greater than 20% of cost or amortized cost, unrealized loss position of 12 or more consecutive months	0
Fixed income securities
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(75,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(21,000,000)
Total unrealized losses	$ (96,000,000)	$ (957,000,000)