Acquisitions, Goodwill, and Acquired Intangible Assets - Summary of Goodwill Activity by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, balance at beginning of period	$ 3,784	$ 3,759
New acquisitions	9,501	60
Other adjustments	65	(35)
Goodwill, balance at end of period	13,350	3,784
North America
Goodwill [Roll Forward]
Goodwill, balance at beginning of period	2,044	2,012
New acquisitions	9,115	30
Other adjustments	6	2
Goodwill, balance at end of period	11,165	2,044
International
Goodwill [Roll Forward]
Goodwill, balance at beginning of period	694	719
New acquisitions	368	13
Other adjustments	46	(38)
Goodwill, balance at end of period	1,108	694
AWS
Goodwill [Roll Forward]
Goodwill, balance at beginning of period	1,046	1,028
New acquisitions	18	17
Other adjustments	13	1
Goodwill, balance at end of period	$ 1,077	$ 1,046