ASC 606 Adoption And Revenue Recognition (Schedule Of Prior Period Impact Of New Accounting Pronouncement) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 778	$ 787	$ 819
Contract acquisition costs	91	87
Other current assets	54	68	64
Property, plant and equipment, net	14,321	14,392	14,377
Other assets	228	224	97
Other current liabilities	334	335	330
Other liabilities	280	308	317
Deferred income taxes	1,217	1,190	1,139
Accumulated deficit	(2,089)	(2,109)	$ (2,263)
Amounts Without Adoption Of ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	810
Other current assets	52
Property, plant and equipment, net	14,297
Other assets	98
Other current liabilities	325
Other liabilities	290
Deferred income taxes	1,164
Accumulated deficit	(2,248)
Accounting Standards Update 2014-09 [Member] | Adjustments For ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	32	(32)
Contract acquisition costs	(91)	87
Other current assets	(2)	4
Property, plant and equipment, net	(24)	15
Other assets	(130)	127
Other current liabilities	(9)	5
Other liabilities	10	(9)
Deferred income taxes	(53)	51
Accumulated deficit	$ (159)	$ 154