Acquisitions, Goodwill, and Acquired Intangible Assets - Allocation of Aggregate Purchase Price of Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Purchase Price
Cash paid, net of cash acquired	$ 2,461	$ 2,186	$ 13,972
Allocation
Goodwill	$ 14,754	$ 14,548	13,350
Acquired intangibles weighted average amortization period	14 years 3 months 18 days
Minimum
Allocation
Intangible assets, estimated useful life		1 year
Maximum
Allocation
Intangible assets, estimated useful life		25 years
Marketing-related
Allocation
Acquired intangibles weighted average amortization period	20 years 8 months 12 days
Contract-based
Allocation
Acquired intangibles weighted average amortization period	10 years 6 months
Technology-based
Allocation
Acquired intangibles weighted average amortization period	3 years 7 months 6 days
Customer-related
Allocation
Acquired intangibles weighted average amortization period	4 years 3 months 18 days
2017 Acquisitions
Purchase Price
Cash paid, net of cash acquired			13,859
Indemnification holdback			104
Aggregate purchase price			13,963
Allocation
Goodwill			9,501
Intangible assets			2,647
Property and equipment			3,810
Deferred tax assets			117
Other assets acquired			1,858
Long-term debt			(1,165)
Deferred tax liabilities			(961)
Other liabilities assumed			(1,844)
Allocated purchase price			$ 13,963
Acquired intangibles weighted average amortization period			21 years
2017 Acquisitions | Minimum
Allocation
Intangible assets, estimated useful life			1 year
2017 Acquisitions | Maximum
Allocation
Intangible assets, estimated useful life			25 years
2017 Acquisitions | Marketing-related
Allocation
Intangible assets			$ 1,987
2017 Acquisitions | Contract-based
Allocation
Intangible assets			440
2017 Acquisitions | Technology-based
Allocation
Intangible assets			166
2017 Acquisitions | Customer-related
Allocation
Intangible assets			$ 54
2018 Acquisitions
Purchase Price
Cash paid, net of cash acquired		$ 1,618
Indemnification holdback		31
Aggregate purchase price		1,649
Allocation
Goodwill		1,228
Intangible assets		677
Property and equipment		11
Deferred tax assets		174
Other assets acquired		282
Long-term debt		(176)
Deferred tax liabilities		(159)
Other liabilities assumed		(388)
Allocated purchase price		$ 1,649
Acquired intangibles weighted average amortization period		6 years
2018 Acquisitions | Minimum
Allocation
Intangible assets, estimated useful life		2 years
2018 Acquisitions | Maximum
Allocation
Intangible assets, estimated useful life		7 years
2018 Acquisitions | Marketing-related
Allocation
Intangible assets		$ 186
2018 Acquisitions | Contract-based
Allocation
Intangible assets		13
2018 Acquisitions | Technology-based
Allocation
Intangible assets		285
2018 Acquisitions | Customer-related
Allocation
Intangible assets		$ 193
2019 Acquisitions
Purchase Price
Cash paid, net of cash acquired	$ 276
Indemnification holdback	39
Aggregate purchase price	315
Allocation
Goodwill	189
Intangible assets	161
Property and equipment	3
Deferred tax assets	29
Other assets acquired	41
Long-term debt	(31)
Deferred tax liabilities	(34)
Other liabilities assumed	(43)
Allocated purchase price	$ 315
Acquired intangibles weighted average amortization period	5 years
2019 Acquisitions | Minimum
Allocation
Intangible assets, estimated useful life	2 years
2019 Acquisitions | Maximum
Allocation
Intangible assets, estimated useful life	7 years
2019 Acquisitions | Marketing-related
Allocation
Intangible assets	$ 8
2019 Acquisitions | Contract-based
Allocation
Intangible assets	0
2019 Acquisitions | Technology-based
Allocation
Intangible assets	139
2019 Acquisitions | Customer-related
Allocation
Intangible assets	$ 14