Recent Accounting Pronouncements (Schedule Of Impact Of Adoption Of ASU 2014-09) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 2,124	$ 2,126	$ 2,162	$ 2,199	$ 2,217	$ 2,251	$ 2,304	$ 2,356	$ 8,611	$ 9,128	$ 8,896
Operating expenses									7,784
Operating income (loss)	$ 127	$ (33)	$ 367	$ 366	$ (1,747)	$ 322	$ (375)	$ 317	827	$ (1,483)	$ 911
Amounts Excluding Adoption of ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									8,596
Operating expenses									7,799
Operating income (loss)									797
Accounting Standards Update 2014-09 [Member] | Impact Of Adoption Of ACS 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue									(15)
Operating expenses									15
Operating income (loss)									$ (30)