Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 9,462	$ 9,119
Cumulative impact from adoption of new revenue accounting standard			$ 3
Other comprehensive income (loss) before reclassifications	46	(26)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(12)	17
Ending balance	11,357	9,462
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(638)	(629)
Ending balance	(601)	(638)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(623)	(659)
Cumulative impact from adoption of new revenue accounting standard			3
Other comprehensive income (loss) before reclassifications	(9)	20
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	0	16
Ending balance	(629)	(623)
Unrealized gain (loss) on available-for- sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	0	1
Cumulative impact from adoption of new revenue accounting standard			0
Other comprehensive income (loss) before reclassifications	10	(1)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(5)	0
Ending balance	5	0
Unrealized gain (loss) on forward contracts
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(15)	29
Cumulative impact from adoption of new revenue accounting standard			$ 0
Other comprehensive income (loss) before reclassifications	45	(45)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(7)	1
Ending balance	$ 23	$ (15)

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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