Goodwill, Customer Relationships and Other Intangible Assets - Schedule of Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 18,870	$ 21,534	$ 28,031
Indefinite-life intangible assets	278	269
Total other intangible assets, net	8,219	9,567
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	6,344	7,596
Accumulated amortization	11,060	9,809
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	1,520	1,599
Accumulated amortization	3,279	2,957
Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	77	103
Accumulated amortization	$ 120	$ 91