Accounts Receivable (Schedule Of Allowance For Doubtful Accounts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts, Beginning of Period	$ 131
Allowance for Doubtful Accounts, End of Period	69	$ 131
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts, Beginning of Period	131	57	$ 72
Charged to Other Revenue	109	164	67
Charged (Credited) to Switched and Nonswitched Revenue and Other Accounts	(22)	15	(17)
Write-offs, net of Recoveries	(149)	(105)	(65)
Allowance for Doubtful Accounts, End of Period	$ 69	$ 131	$ 57