Accounts Receivable - Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance as of January 1,	$ 72	$ 47
Provision for doubtful accounts	11	12
Bad debt write-offs	(4)	(13)
Balance as of March 31,	79	$ 58
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2016-13
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance as of January 1,	$ 12