Accounts Receivable (Schedule Of Allowance For Doubtful Accounts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts, Beginning of the Period	$ 120	$ 105	$ 69
Adjustments	106	109	93
Increases: Charged to Revenue	106	109	93
Decreases: Write-offs and Customer Credits	(96)	(83)	(89)
Reclassified to Assets Held for Sale		(11)
Allowance for Doubtful Accounts, End of the Period	$ 130	$ 120	105
Impact Of Adoption Of ACS 606 [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Adjustments			$ 32