Stockholders' Equity - Changes in Each Component of AOCI of the Parent (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,				$ (1,342)
Other comprehensive income (loss):
Holding gain(loss) on net investment hedge				1
Balance,		$ (1,385)		(1,385)
Accounting Standards Update 2016-01 [Member]
Other comprehensive income (loss):
Adoption of ASU 2016-01 financial instruments adjustment, January 1, 2018						$ 2
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(661)	$ (617)	(670)	$ (646)
Other comprehensive income (loss):
Currency translation adjustments		(54)	(32)	(40)	2
Holding gain(loss) on net investment hedge		5	(3)		(8)
Tax (expense) benefit
Other comprehensive income (loss)		(49)	(35)	(40)	(6)
Balance,		(710)	(652)	(710)	(652)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(72)	(38)	(64)	(34)
Other comprehensive income (loss):
Holding gains and losses		58	(63)	20	(75)
Reclassification of amount to net income	[1]	(64)	68	(35)	74
Tax (expense) benefit				1	2
Other comprehensive income (loss)		(6)	5	(14)	1
Balance,		(78)	(33)	(78)	(33)
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		0	0	2	0
Other comprehensive income (loss):
Holding gains and losses
Reclassification of amount to net income	[1]
Tax (expense) benefit
Other comprehensive income (loss)		0	0	0	0
Balance,		0	0	0	0
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
Other comprehensive income (loss):
Adoption of ASU 2016-01 financial instruments adjustment, January 1, 2018						(2)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(603)	(599)	(610)	(604)
Other comprehensive income (loss):
Reclassification adjustment for net actuarial losses included in net periodic benefit cost	[2]	8	7	17	15
Tax (expense) benefit		(2)	(2)	(4)	(5)
Other comprehensive income (loss)		6	5	13	10
Balance,		(597)	(594)	(597)	(594)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(1,336)	(1,254)	(1,342)	(1,284)
Other comprehensive income (loss):
Currency translation adjustments		(54)	(32)	(40)	2
Holding gain(loss) on net investment hedge		5	(3)		(8)
Holding gains and losses		58	(63)	20	(75)
Reclassification of amount to net income	[1]	(64)	68	(35)	74
Reclassification adjustment for net actuarial losses included in net periodic benefit cost	[2]	8	7	17	15
Tax (expense) benefit		(2)	(2)	(3)	(3)
Other comprehensive income (loss)		(49)	(25)	(41)	5
Balance,		$ (1,385)	$ (1,279)	$ (1,385)	$ (1,279)
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
Other comprehensive income (loss):
Adoption of ASU 2016-01 financial instruments adjustment, January 1, 2018						$ (2)

[1] For 2018, realized gains and losses from currency-related forward contracts associated with forecasted transactions or from other derivative instruments treated as cash flow hedges are reclassified from AOCI into the same line item in the consolidated statement of operations in which the underlying forecasted transaction or other hedged item is recorded. See Note 14 for additional details. For 2017, reclassifications from AOCI were included in other expense, net.

[2] See Note 11 for additional details.