Goodwill, Customer Relationships and Other Intangible Assets - Rollforward Goodwill (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
	Oct. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
As of January 1, 2019		$ 28,031		$ 30,475	$ 28,031	$ 30,475
January 2019 reorganization					0
Effect of foreign currency rate change and other					9	(58)
Impairments	$ (2,700)	(6,500)	$ (2,700)	(2,700)	(6,506)	(2,726)	$ 0
As of December 31, 2019			28,031		21,534	28,031	30,475
International and Global Accounts
Goodwill [Line Items]
As of January 1, 2019		3,595			3,595
January 2019 reorganization					0
Effect of foreign currency rate change and other					9
Impairments					(934)
As of December 31, 2019			3,595		2,670	3,595
Enterprise
Goodwill [Line Items]
As of January 1, 2019		5,222			5,222
January 2019 reorganization					987
Effect of foreign currency rate change and other					0
Impairments					(1,471)
As of December 31, 2019			5,222		4,738	5,222
Small and Medium Business
Goodwill [Line Items]
As of January 1, 2019		5,193			5,193
January 2019 reorganization					(1,038)
Effect of foreign currency rate change and other					0
Impairments					(896)
As of December 31, 2019			5,193		3,259	5,193
Wholesale
Goodwill [Line Items]
As of January 1, 2019		6,437			6,437
January 2019 reorganization					395
Effect of foreign currency rate change and other					0
Impairments					(3,019)
As of December 31, 2019			6,437		3,813	6,437
Consumer
Goodwill [Line Items]
As of January 1, 2019		$ 7,584		$ 10,278	7,584	10,278
January 2019 reorganization					(344)
Effect of foreign currency rate change and other					0
Impairments					(186)	(2,726)
As of December 31, 2019			$ 7,584		$ 7,054	$ 7,584	$ 10,278