Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 1,845
Other comprehensive income (loss) before reclassifications, net of tax	14	$ 33
Less: Amounts reclassified from AOCI, net of tax	(1)	0
Other comprehensive income, net of tax	15	33
Ending balance	1,839
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	16	27
Other comprehensive income (loss) before reclassifications, net of tax	0	(6)
Less: Amounts reclassified from AOCI, net of tax	0	0
Other comprehensive income, net of tax	0	(6)
Ending balance	16	21
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(297)	(246)
Other comprehensive income (loss) before reclassifications, net of tax	2	(1)
Less: Amounts reclassified from AOCI, net of tax	(1)	0
Other comprehensive income, net of tax	3	(1)
Ending balance	(294)	(247)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(108)	(166)
Other comprehensive income (loss) before reclassifications, net of tax	12	40
Less: Amounts reclassified from AOCI, net of tax	0	0
Other comprehensive income, net of tax	12	40
Ending balance	(96)	(126)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(389)	(385)
Ending balance	$ (374)	$ (352)