Investments Investments - Gross Unrealized Losses by Unrealized Loss Position and Credit Quality (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Unrealized losses related to securities with unrealized loss position greater than or equal to 20% of amortized cost or cost, greater than 12 months	$ 1
Investment grade fixed income securities
Schedule of Held-to-maturity Securities [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(20)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(12)
Total unrealized losses	(32)	$ (268)
Below investment grade fixed income securities
Schedule of Held-to-maturity Securities [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(19)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(4)
Total unrealized losses	(23)	(121)
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	7
Fixed income securities
Schedule of Held-to-maturity Securities [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(39)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(16)
Total unrealized losses	$ (55)	$ (389)