Accumulated Other Comprehensive Income (Loss) (AOCI) Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	$ (205)	$ (150)	$ (136)
Other comprehensive (loss) income before reclassifications	15	(37)	4
Amounts reclassified from AOCI	(9)	(18)	(18)
Net current period other comprehensive (loss) income	6	(55)	(14)
Accumulated other comprehensive income (loss), ending balance	(199)	(205)	(150)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	(224)	(172)	(125)
Other comprehensive (loss) income before reclassifications	41	(52)	(47)
Amounts reclassified from AOCI	0	0	0
Net current period other comprehensive (loss) income	41	(52)	(47)
Accumulated other comprehensive income (loss), ending balance	(183)	(224)	(172)
Changes in Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	6	23	(8)
Other comprehensive (loss) income before reclassifications	(13)	(1)	43
Amounts reclassified from AOCI	(8)	(16)	(12)
Net current period other comprehensive (loss) income	(21)	(17)	31
Accumulated other comprehensive income (loss), ending balance	(15)	6	23
Changes in Fair Value of Effective Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive income (loss), beginning balance	13	(1)	(3)
Other comprehensive (loss) income before reclassifications	(13)	16	8
Amounts reclassified from AOCI	(1)	(2)	(6)
Net current period other comprehensive (loss) income	(14)	14	2
Accumulated other comprehensive income (loss), ending balance	$ (1)	$ 13	$ (1)