Comprehensive (Loss) Income (Schedule Of Reclassifications Out Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Provision for income taxes	$ 2	$ (3)
Net Income	14	70
Unrealized Gains (Losses) on Derivatives | Amount Reclassified from Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net losses on derivatives
Provision for income taxes
Net Income	1
Unrealized Gains (Losses) on Derivatives | Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Fuel swap contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) on derivatives:		(1)
Unrealized Gains (Losses) on Derivatives | Amount Reclassified from Accumulated Other Comprehensive Income (Loss) | Interest rate swap contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains (losses) on derivatives:	$ 1	$ 1