Goodwill, Customer Relationships and Other Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0	$ 3,700	$ 0	$ 3,708	$ 0
Acquired finite-lived intangible asset amortization expense	206		$ 204	604	$ 595
Intangible assets, gross, including goodwill	$ 16,400			$ 16,400

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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