Summary Of Significant Accounting Policies (Schedule Of New Accounting Pronouncement Adoption) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 2,126	$ 2,251	$ 6,487	$ 6,911
Operating expenses	2,159	1,929	5,787	6,647
Operating income (loss)	(33)	$ 322	700	$ 264
Amounts Excluding Adoption Of ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	2,120		6,473
Operating expenses	2,162		5,797
Operating income (loss)	(42)		676
Accounting Standards Update 2014-09 [Member] | Impact Of Adoption Of ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	(6)		(14)
Operating expenses	3		10
Operating income (loss)	$ (9)		$ (24)