Significant Accounting Policies - Summary of Changes in Allowance for Credit Losses (Details) - Allowance for Doubtful Accounts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance, beginning of period	$ 25	$ 21	$ 16
Provision charged to expense	17	11	11
Write-offs, net of recoveries and other adjustments	(9)	(7)	(6)
Balance, end of period	$ 33	$ 25	$ 21