ASC 606 Adoption And Revenue Recognition (Schedule Of Prior Period Impact Of New Accounting Pronouncement) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 751	$ 787	$ 819
Contract acquisition costs	97	87
Other current assets	106	68	64
Property, plant and equipment, net	14,282	14,392	14,377
Other assets	236	224	97
Other current liabilities	387	335	330
Other liabilities	274	308	317
Deferred income taxes	1,219	1,190	1,139
Accumulated deficit	(2,107)	(2,109)	$ (2,263)
Amounts Excluding Adoption Of ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	786
Other current assets	104
Property, plant and equipment, net	14,243
Other assets	99
Other current liabilities	375
Other liabilities	279
Deferred income taxes	1,165
Accumulated deficit	(2,280)
Accounting Standards Update 2014-09 [Member] | Impact Of Adoption Of ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	35	(32)
Contract acquisition costs	(97)	87
Other current assets	(2)	4
Property, plant and equipment, net	(39)	15
Other assets	(137)	127
Other current liabilities	(12)	5
Other liabilities	5	(9)
Deferred income taxes	(54)	51
Accumulated deficit	$ (173)	$ 154