Stockholders' Equity - Changes in Each Component of AOCI of the Parent (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,				$ (1,362)
Other comprehensive income (loss):
Balance,		$ (994)		(994)
Accounting Standards Update 2016-01 [Member]
Other comprehensive income (loss):
Adoption of ASU 2016-01 financial instruments adjustment, January 1, 2018						$ 0
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(694)	$ (710)	(721)	$ (670)
Other comprehensive income (loss):
Currency translation adjustments		(39)	(15)	(12)	(55)
Holding loss on net investment hedge			(3)		(3)
Tax (expense) benefit
Other comprehensive income (loss)		(39)	(18)	(12)	(58)
Balance,		(733)	(728)	(733)	(728)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(47)	(78)	(54)	(64)
Other comprehensive income (loss):
Holding gains and losses		57	9	77	29
Reclassification of amount to net income	[1]	(49)	(7)	(62)	(42)
Tax (expense) benefit			1		2
Other comprehensive income (loss)		8	3	15	(11)
Balance,		(39)	(75)	(39)	(75)
Accumulated Net Gain (Loss) from Investments Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		0	0	0	2
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 Gain (Loss) from Investments 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,		(227)	(597)	(587)	(610)
Other comprehensive income (loss):
Net actuarial gain			18	104	18
Reclassification adjustment for net actuarial losses included in net periodic benefit cost	[2]	6	9	282	26
Tax (expense) benefit		(1)	(6)	(21)	(10)
Other comprehensive income (loss)		5	21	365	34
Balance,		(222)	(576)	(222)	(576)
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance,		(968)	(1,385)	(1,362)	(1,342)
Other comprehensive income (loss):
Currency translation adjustments		(39)	(15)	(12)	(55)
Holding loss on net investment hedge			(3)		(3)
Holding gains and losses		57	9	77	29
Reclassification of amount to net income	[1]	(49)	(7)	(62)	(42)
Net actuarial gain			18	104	18
Reclassification adjustment for net actuarial losses included in net periodic benefit cost	[2]	6	9	282	26
Tax (expense) benefit		(1)	(5)	(21)	(8)
Other comprehensive income (loss)		(26)	6	368	(35)
Balance,		$ (994)	$ (1,379)	$ (994)	$ (1,379)
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] 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 15 for additional details.

[2] See Note 12 for additional details.