Basis of Presentation and Significant Accounting Policies - Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 52	$ 42	$ 26
Provision charged to expense	34	36	24
Write-offs, less recoveries, and other adjustments	(28)	(26)	(8)
Ending balance	$ 58	$ 52	$ 42