Revenue Recognition - Impact of Adoption on Balance Sheet and Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other long-term liabilities	$ 160	$ 160	$ 354
Accumulated deficit	(16,173)	(16,173)	$ (16,525)
Revenue from contracts with customers	1,331	3,924
Marketing [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	1,219	3,738
Marketing	1,238	3,798
Calculated under revenue guidance in effect before Topic 606 [Member] \| Marketing [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	1,508	4,320
Marketing	1,516	4,365
Difference between revenue guidance in effect before and after Topic 606 [Member] \| Marketing [Member] \| ASU 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	(289)	(582)
Marketing	$ (278)	$ (567)

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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