Goodwill, Customer Relationships and Other Intangible Assets - Additional Information (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)	Jan. 01, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Control premium, percent		4.10%				4.50%
Goodwill impairment	$ 0	$ 6,500	$ 0	$ 6,506	$ 0
Amortization of intangible assets	438		$ 446	1,300	$ 1,300
Intangible assets, gross (including goodwill)	$ 43,800			$ 43,800
Number of reportable segments \| segment				5

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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