Investments - Gross unrealized losses by unrealized loss position and credit quality (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Investment grade fixed income securities
Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	$ (85,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	0
Total unrealized losses	85,000,000	$ 8,000,000
Below investment grade fixed income securities
Investments [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	24,000,000
Unrealized losses having loss of less than twenty percent, less than 12 months	(12,000,000)
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
Investments [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost, net	(100,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost, net	(15,000,000)
Total unrealized losses	$ 115,000,000	$ 32,000,000