Goodwill, Customer Relationships and Other Intangible Assets - Rollforward Goodwill (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Oct. 31, 2020	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill Activity
As of beginning of period		$ 28,031	$ 21,534	$ 28,031
January 2019 reorganization				0
Effect of foreign currency exchange rate change and other			(22)	9
Impairment	$ (2,600)	(6,500)	(2,642)	(6,506)	$ (2,726)
As of end of period			18,870	21,534	28,031
Goodwill accumulated impairment loss			12,900	10,300	3,800
Business
Goodwill Activity
As of beginning of period		20,447		20,447
As of end of period					20,447
Consumer
Goodwill Activity
As of beginning of period		7,584		7,584
As of end of period					7,584
International and Global Accounts
Goodwill Activity
As of beginning of period		3,595	2,670	3,595
January 2019 reorganization				0
Effect of foreign currency exchange rate change and other			(15)	9
Impairment			(100)	(934)
As of end of period			2,555	2,670	3,595
Enterprise
Goodwill Activity
As of beginning of period		5,222	4,738	5,222
January 2019 reorganization				987
Effect of foreign currency exchange rate change and other			0	0
Impairment			0	(1,471)
As of end of period			4,738	4,738	5,222
Small and Medium Business
Goodwill Activity
As of beginning of period		5,193	3,259	5,193
January 2019 reorganization				(1,038)
Effect of foreign currency exchange rate change and other			(7)	0
Impairment			(444)	(896)
As of end of period			2,808	3,259	5,193
Wholesale
Goodwill Activity
As of beginning of period		6,437	3,813	6,437
January 2019 reorganization				395
Effect of foreign currency exchange rate change and other			0	0
Impairment			(699)	(3,019)
As of end of period			3,114	3,813	6,437
Consumer
Goodwill Activity
As of beginning of period		$ 7,584	7,054	7,584
January 2019 reorganization				(344)
Effect of foreign currency exchange rate change and other			0	0
Impairment			(1,399)	(186)
As of end of period			$ 5,655	$ 7,054	$ 7,584