Fair Value Measurements (Schedule Of Reconciliation Of The Beginning And Ending Fair Values Of Financial Instruments Valued Using Significant Unobservable Inputs (Level 3) On A Recurring Basis) (Details) - Fuel swap contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reconciliation of the beginning and ending fair values of financial instruments valued using significant unobservable inputs (Level 3)
Balance at the beginning of the period	$ 1	$ (4)
Total gains (losses) (realized and unrealized)
Included in earnings		1
Included in other comprehensive income	(9)	4
Settlements		(1)
Balance at the end of the period	$ (8)