Goodwill, Customer Relationships and Other Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Control premium, percent	4.10%
Goodwill impairment	$ 6,506	$ 0
Amortization of intangible assets	429	$ 444
Intangible assets, gross (including goodwill)	$ 43,600

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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