Comprehensive (Loss) Income (Schedule Of Reclassifications Out Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Impact of income taxes	$ (15)			$ (4)			$ (31)	$ (22)
Net (Loss) Income	(7)	$ 53	$ 14	25	$ 59	$ 70	61	154
Amount Reclassified From Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on derivatives	(2)			1			(4)	4
Impact of income taxes	1						2
Net (Loss) Income	(2)			1			(3)	3
Amount Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Fuel Swap Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on derivatives	(1)						(3)
Amount Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Interest Rate Swap Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains (losses) on derivatives	$ (1)			$ 1			$ (2)	$ 4