Goodwill, Customer Relationships and Other Intangible Assets - Rollforward of Goodwill (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
As of beginning of period	$ 18,870
Reclassified as held for sale	(2,864)
Effect of foreign currency exchange rate change and other	(19)
As of end of period	15,987
Accumulated impairment losses	7,700	$ 12,900
Disposal Group, Held-for-sale, Not Discontinued Operations
Goodwill [Roll Forward]
Reclassified as held for sale	(2,900)
International and Global Accounts
Goodwill [Roll Forward]
As of beginning of period	2,555
Enterprise
Goodwill [Roll Forward]
As of beginning of period	4,738
Small and Medium Business
Goodwill [Roll Forward]
As of beginning of period	2,808
Wholesale
Goodwill [Roll Forward]
As of beginning of period	3,114
Consumer
Goodwill [Roll Forward]
As of beginning of period	5,655
Business
Goodwill [Roll Forward]
Reclassified as held for sale	(918)
Effect of foreign currency exchange rate change and other	0
As of end of period	11,236
Mass Markets
Goodwill [Roll Forward]
Reclassified as held for sale	(1,946)
Effect of foreign currency exchange rate change and other	(19)
As of end of period	$ 4,751