Goodwill, Customer Relationships and Other Intangible Assets (Details) - USD ($) $ in Millions		12 Months Ended
	Nov. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill		$ 30,475	$ 19,650	$ 20,742
Indefinite-life intangible assets		269	269
Other intangible assets, net		1,897	1,531
Intangible assets, net (including goodwill)		$ 20,060
Acquired finite-lived intangible assets, weighted average useful life	12 years	12 years
Amortization expense for intangible assets		$ 1,226	1,225	$ 1,353
Gross carrying amount of intangible assets		52,669
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		10,876	2,797
Accumulated amortization		$ 7,096	6,318
Acquired finite-lived intangible assets, weighted average useful life		12 years
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		$ 1,469	1,227
Accumulated amortization		$ 2,294	2,019
Acquired finite-lived intangible assets, weighted average useful life		5 years
Tradenames and patents
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		$ 159	35
Accumulated amortization		$ 31	$ 23
Acquired finite-lived intangible assets, weighted average useful life		5 years