Goodwill, Customer Relationships and Other Intangible Assets - Rollforward of Goodwill (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Goodwill [Roll Forward]
As of December 31, 2019	$ 21,534
Effect of foreign currency exchange rate change and other	(58)
As of September 30, 2020	21,476
International and Global Accounts
Goodwill [Roll Forward]
As of December 31, 2019	2,670
Effect of foreign currency exchange rate change and other	(51)
As of September 30, 2020	2,619
Enterprise
Goodwill [Roll Forward]
As of December 31, 2019	4,738
Effect of foreign currency exchange rate change and other	0
As of September 30, 2020	4,738
Small and Medium Business
Goodwill [Roll Forward]
As of December 31, 2019	3,259
Effect of foreign currency exchange rate change and other	(7)
As of September 30, 2020	3,252
Wholesale
Goodwill [Roll Forward]
As of December 31, 2019	3,813
Effect of foreign currency exchange rate change and other	0
As of September 30, 2020	3,813
Consumer
Goodwill [Roll Forward]
As of December 31, 2019	7,054
Effect of foreign currency exchange rate change and other	0
As of September 30, 2020	$ 7,054