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Recent Accounting Literature (Schedule Of Impact Of Adoption Of ASU 2017-07) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Network related expenses $ 476 $ 498 $ 1,437 $ 1,468
Selling, general and administrative expenses 445 487 1,374 1,560
Investment and other income, net 3 4 16 4
Pension settlement costs $ 9 15 $ 34 77
Previously Reported [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Network related expenses   497   1,468
Selling, general and administrative expenses   486   1,561
Pension settlement costs   15   77
Investment and other income, net   2   5
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   1   (1)
Pension settlement costs   (15)   (77)
Investment and other income, net   2   (1)
Pension settlement costs   $ 15   $ 77