Revenues - Trade Accounts And Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 57	$ 67
Credit loss expense	5	18
Write-offs charged against the allowance	(12)	(11)
Ending Balance	$ 50	73
Cumulative Effect, Period of Adoption, Adjustment
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance		$ (1)