Goodwill, Customer Relationships and Other Intangible Assets - Rollforward of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Goodwill [Roll Forward]
As of December 31, 2018		$ 28,031		$ 28,031
January 2019 reorganization				0
Effect of foreign currency rate change and other				(18)
Impairment of goodwill	$ 0	(6,500)	$ 0	(6,506)	$ 0
As of September 30, 2019	21,507			21,507
International and Global Accounts
Goodwill [Roll Forward]
As of December 31, 2018		3,595		3,595
January 2019 reorganization				0
Effect of foreign currency rate change and other				(18)
Impairment of goodwill				(934)
As of September 30, 2019	2,643			2,643
Enterprise
Goodwill [Roll Forward]
As of December 31, 2018		5,222		5,222
January 2019 reorganization				987
Effect of foreign currency rate change and other				0
Impairment of goodwill				(1,471)
As of September 30, 2019	4,738			4,738
Small and Medium Business
Goodwill [Roll Forward]
As of December 31, 2018		5,193		5,193
January 2019 reorganization				(1,038)
Effect of foreign currency rate change and other				0
Impairment of goodwill				(896)
As of September 30, 2019	3,259			3,259
Wholesale
Goodwill [Roll Forward]
As of December 31, 2018		6,437		6,437
January 2019 reorganization				395
Effect of foreign currency rate change and other				0
Impairment of goodwill				(3,019)
As of September 30, 2019	3,813			3,813
Consumer
Goodwill [Roll Forward]
As of December 31, 2018		$ 7,584		7,584
January 2019 reorganization				(344)
Effect of foreign currency rate change and other				0
Impairment of goodwill				(186)
As of September 30, 2019	$ 7,054			$ 7,054