Acquisitions, Goodwill, and Acquired Intangible Assets - Summary of Goodwill Activity by Segment (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Goodwill [Line Items]
Goodwill	$ 13,944	$ 13,350
Goodwill, Acquired During Period	607
Goodwill, Translation and Purchase Accounting Adjustments	(13)
North America
Goodwill [Line Items]
Goodwill	11,571	11,165
Goodwill, Acquired During Period	409
Goodwill, Translation and Purchase Accounting Adjustments	(3)
International
Goodwill [Line Items]
Goodwill	1,288	1,108
Goodwill, Acquired During Period	183
Goodwill, Translation and Purchase Accounting Adjustments	(3)
AWS
Goodwill [Line Items]
Goodwill	1,085	$ 1,077
Goodwill, Acquired During Period	15
Goodwill, Translation and Purchase Accounting Adjustments	$ (7)