Acquisitions, Goodwill, and Acquired Intangible Assets - Acquired Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangibles, Gross	$ 4,422	$ 1,900
Accumulated Amortization	(1,051)	(1,046)
Acquired Intangibles, Net	$ 3,371	854
Weighted Average Life Remaining	17 years 9 months
Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets, estimated useful life	1 year
Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets, estimated useful life	25 years
Marketing-related
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangibles, Gross	$ 2,486	499
Accumulated Amortization	(418)	(299)
Acquired Intangibles, Net	$ 2,068	200
Weighted Average Life Remaining	23 years
Contract-based
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangibles, Gross	$ 1,013	397
Accumulated Amortization	(213)	(212)
Acquired Intangibles, Net	$ 800	185
Weighted Average Life Remaining	13 years
Technology- and content-based
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangibles, Gross	$ 640	705
Accumulated Amortization	(252)	(353)
Acquired Intangibles, Net	$ 388	352
Weighted Average Life Remaining	4 years 5 months
Customer-related
Acquired Finite-Lived Intangible Assets [Line Items]
Acquired Intangibles, Gross	$ 283	299
Accumulated Amortization	(168)	(182)
Acquired Intangibles, Net	$ 115	$ 117
Weighted Average Life Remaining	2 years 1 month