Investments - Gross Unrealized Losses by Unrealized Loss Position and Credit Quality (Details) - USD ($)	Sep. 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	$ 0
Total
Schedule of Held-to-maturity Securities [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(28,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(16,000,000)
Total unrealized losses	(44,000,000)	$ (389,000,000)
Investment grade
Schedule of Held-to-maturity Securities [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(8,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(13,000,000)
Total unrealized losses	(21,000,000)	(268,000,000)
Below investment grade
Schedule of Held-to-maturity Securities [Line Items]
Fixed income securities with unrealized loss position less than 20% of amortized cost	(20,000,000)
Fixed income securities with unrealized loss position greater than or equal to 20% of amortized cost	(3,000,000)
Total unrealized losses	(23,000,000)	$ (121,000,000)
Available for sale securities, unrealized losses having loss of less than twenty percent, less than 12 months	$ (7,000,000)