Revenue Recognition - Impact of Adoption on Balance Sheet and Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current liabilities	$ 1,277	$ 1,277	$ 1,455
Other long-term liabilities	177	177	354
Accumulated deficit	(16,257)	(16,257)	$ (16,525)
Revenue from contracts with customers	1,233	2,593
Marketing [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	1,273	2,519
Marketing	1,292	2,560
Calculated under revenue guidance in effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current liabilities	1,275	1,275
Other long-term liabilities	172	172
Accumulated deficit	(16,249)	(16,249)
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	1,449	2,810
Marketing	1,469	2,852
Difference between revenue guidance in effect before and after Topic 606 [Member] | ASU 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Other current liabilities	2	2
Other long-term liabilities	5	5
Accumulated deficit	(8)	(8)
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	(176)	(291)
Marketing	$ (177)	$ (292)