Goodwill, Customer Relationships and Other Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 9,360	$ 9,360
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	783	893
Accumulated amortization	4,916	4,806
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	355	311
Accumulated amortization	$ 1,724	$ 1,712