Stockholders' Equity - Changes in Each Component of AOCI of the Parent (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,				$ (1,284)
Other comprehensive income (loss):
Holding loss on net investment hedge				(8)
Balance,		$ (1,277)		(1,277)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(652)	$ (603)	(646)	$ (608)
Other comprehensive income (loss):
Currency translation adjustments		(3)	(8)	(1)	(3)
Holding loss on net investment hedge				(8)
Tax (expense) benefit
Other comprehensive income (loss)		(3)	(8)	(9)	(3)
Balance,		(655)	(611)	(655)	(611)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(33)	(14)	(34)	(4)
Other comprehensive income (loss):
Holding gains and losses		(48)	(17)	(123)	(30)
Reclassification of amount to net income	[1]	35	6	109	9
Tax (expense) benefit		(1)		1
Other comprehensive income (loss)		(14)	(11)	(13)	(21)
Balance,		(47)	(25)	(47)	(25)
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		0	5	0	2
Other comprehensive income (loss):
Holding gains and losses			2		5
Reclassification of amount to net income	[1]		(7)		(7)
Tax (expense) benefit
Other comprehensive income (loss)		0	(5)	0	(2)
Balance,		0	0	0	0
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(594)	(551)	(604)	(564)
Other comprehensive income (loss):
Actuarial gain (loss) on census update		21	(6)	21	(6)
Reclassification adjustment for net actuarial losses included in net periodic benefit cost	[2]	7	7	22	20
Tax (expense) benefit		(9)	(1)	(14)	(1)
Other comprehensive income (loss)		19	0	29	13
Balance,		(575)	(551)	(575)	(551)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(1,279)	(1,163)	(1,284)	(1,174)
Other comprehensive income (loss):
Currency translation adjustments		(3)	(8)	(1)	(3)
Holding loss on net investment hedge				(8)
Holding gains and losses		(48)	(15)	(123)	(25)
Reclassification of amount to net income	[1]	35	(1)	109	2
Actuarial gain (loss) on census update		21	(6)	21	(6)
Reclassification adjustment for net actuarial losses included in net periodic benefit cost	[2]	7	7	22	20
Tax (expense) benefit		(10)	(1)	(13)	(1)
Other comprehensive income (loss)		2	(24)	7	(13)
Balance,		$ (1,277)	$ (1,187)	$ (1,277)	$ (1,187)

[1] Foreign currency contract and investment reclassifications are included in Other income (expense), net.

[2] See Note 10 for additional details.