Goodwill, Customer Relationships and Other Intangible Assets - Rollforward of Goodwill (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($)
Goodwill [Roll Forward]
As of beginning of period	$ 18,870
Effect of foreign currency exchange rate change and other	(16)
As of end of period	18,854
Accumulated impairment losses	12,900
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]
Effect of foreign currency exchange rate change and other	(16)
As of end of period	12,157
Mass Markets
Goodwill [Roll Forward]
Effect of foreign currency exchange rate change and other	0
As of end of period	$ 6,697