Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Investment [Line Items]
Total unrealized losses	$ 1,000,000
Investment grade
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	(15,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(15,000,000)
Total unrealized losses	30,000,000	$ 61,000,000
Below investment grade
Investment [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	(24,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(19,000,000)
Total unrealized losses	43,000,000	35,000,000
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	(17,000,000)
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, net	(39,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(34,000,000)
Total unrealized losses	$ 73,000,000	$ 96,000,000