Goodwill, Customer Relationships and Other Intangible Assets - Schedule of Goodwill, Customer Relationships, and Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 21,526	$ 28,031
Finite-lived intangible assets, net	8,580	8,911
Indefinite-life intangible assets	269	269
Total other intangible assets, net	1,929	1,868
Customer relationships
Goodwill [Line Items]
Finite-lived intangible assets, net	8,580	8,911
Accumulated amortization	8,825	8,492
Computer Software, Intangible Asset
Goodwill [Line Items]
Finite-lived intangible assets, net	1,536	1,468
Accumulated amortization	2,678	2,616
Trade Names and Patents
Goodwill [Line Items]
Finite-lived intangible assets, net	124	131
Accumulated amortization	$ 69	$ 61