Goodwill, Customer Relationships and Other Intangible Assets - Additional Information (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jan. 31, 2019	Jan. 01, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Control premium, percent						4.10%	4.50%
Goodwill impairment	$ 0	$ 0	$ 6,500	$ 0	$ 6,506
Amortization of intangible assets	443	$ 438		1,300	$ 1,300
Intangible assets, gross (including goodwill)	$ 44,100			$ 44,100
Minimum | Revenue Multiple
Goodwill [Line Items]
Goodwill impairment, measurement input			2.1
Minimum | EBITDA Multiple
Goodwill [Line Items]
Goodwill impairment, measurement input			4.9
Maximum | Revenue Multiple
Goodwill [Line Items]
Goodwill impairment, measurement input			4.9
Maximum | EBITDA Multiple
Goodwill [Line Items]
Goodwill impairment, measurement input			9.8