Income Taxes - Valuation Allowances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Valuation allowance, deferred tax assets	$ 0	$ 0
Tax valuation allowance allocated to Net income (loss)
Valuation Allowance [Line Items]
Valuation allowance, deferred tax assets	128	119
Increase (decrease) in valuation allowance	9	(5)	$ (2)
Tax valuation allowance allocated to Other comprehensive income
Valuation Allowance [Line Items]
Valuation allowance, deferred tax assets	(128)	(119)
Increase (decrease) in valuation allowance	$ (9)	$ 0	$ 0