Recent Accounting Literature (Schedule Of Impact Of Adoption Of ASU 2017-07) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Network related expenses	$ 478	$ 477	$ 961	$ 970
Selling, general and administrative expenses	460	531	929	1,073
Investment and other income, net	5		13
Pension settlement costs	$ 25	19	$ 25	62
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Network related expenses		477		971
Selling, general and administrative expenses		531		1,075
Pension settlement costs		19		62
Investment and other income, net				3
Accounting Standards Update 2017-07 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Network related expenses				(1)
Selling, general and administrative expenses				(2)
Pension settlement costs		(19)		(62)
Investment and other income, net				(3)
Pension settlement costs		$ 19		$ 62