Accumulated Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	$ 5,602		$ 5,602		$ 4,874
Accumulated other comprehensive income (loss)	(24)	$ (13)	(24)	$ (13)	7	$ (121)
Other comprehensive income (loss)	9	40	(33)	110
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	52	30	52	30	43	29
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			20	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(11)	1
Other comprehensive income (loss)			9	1
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' Equity Attributable to Parent	$ (76)	$ (43)	(76)	(43)	$ (36)	$ (150)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(40)	107
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			0	0
Other comprehensive income (loss)			(40)	107
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(20)	107
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			(11)	1
Other comprehensive income (loss)			$ (31)	$ 108