Revenues - Trade Accounts And Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 57	$ 67
Credit loss expense	1	18
Write-offs charged against the allowance	(9)	(9)
Ending Balance	$ 49	75
Cumulative Effect, Period of Adoption, Adjustment
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance		$ (1)