Income Taxes - Valuation Allowances Against Deferred Tax Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowances Against Deferred Tax Assets
Settlement of tax matters with Former Parent1	$ (101)	$ 0
Deferred tax asset valuation allowance
Valuation Allowances Against Deferred Tax Assets
Allowances at beginning of year	150	90
Allowances at end of year	125	150
Deferred tax asset valuation allowance | Benefits reserved current year
Valuation Allowances Against Deferred Tax Assets
Benefits reserved current year	83	98
Deferred tax asset valuation allowance | Benefits recognized current year
Valuation Allowances Against Deferred Tax Assets
Benefits recognized current year	0	(4)
Deferred tax asset valuation allowance | Change in Tax rate /impact of U.S. tax reform
Valuation Allowances Against Deferred Tax Assets
Change in Tax rate /impact of U.S. tax reform	(4)	(35)
Deferred tax asset valuation allowance | Translation difference
Valuation Allowances Against Deferred Tax Assets
Translation difference	$ (3)	$ 1