Goodwill, Customer Relationships and Other Intangible Assets - Additional Information (Details) $ in Millions			12 Months Ended
	Oct. 31, 2018 reporting_unit	Oct. 31, 2017 reporting_unit	Dec. 31, 2018 USD ($) reporting_unit	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net			$ 19,100
Acquired finite-lived intangible assets, weighted average useful life			11 years
Amortization of intangible assets			$ 1,800	$ 1,200	$ 1,200
Intangible assets, gross			50,000
Control premium, percent	0.10%
Goodwill impairment			$ 2,726	0	0
Number of reporting units | reporting_unit	5	3	5
Goodwill			$ 28,031	30,475	19,650
Medium and Small Business
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment percent	2.00%
Enterprise
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment percent	11.00%
International and Global Accounts
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment percent	30.00%
Wholesale and Indirect
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment percent	5.00%
Business
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment			0
Goodwill			20,447	$ 20,197	$ 9,372
Business | Medium and Small Business
Finite-Lived Intangible Assets [Line Items]
Goodwill			5,193
Business | Enterprise
Finite-Lived Intangible Assets [Line Items]
Goodwill			5,222
Business | International and Global Accounts
Finite-Lived Intangible Assets [Line Items]
Goodwill			3,596
Business | Wholesale and Indirect
Finite-Lived Intangible Assets [Line Items]
Goodwill			$ 6,436
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			11 years
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			3 years
Tradenames and patents
Finite-Lived Intangible Assets [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			4 years