Fair Value Measurements (Schedule Of The Carrying Amount And Estimated Fair Value Of The Company's Financial Instruments That Are Recorded At Fair Value On A Recurring Basis) (Details) - Recurring - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Quoted Price In Active Markets (Level 1)
Financial Assets:
Deferred compensation trust	$ 12	$ 13
Total financial assets	12	13
Significant Other Observable Inputs (Level 2)
Financial Assets:
Derivative asset, current	2
Net investment hedge	3
Total financial assets	6	5
Total financial liabilities	33	1
Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Financial Assets:
Derivative asset, current		5
Derivative contracts	33	1
Significant Unobservable Inputs (Level 3)
Financial Assets:
Total financial assets		1
Total financial liabilities	8
Significant Unobservable Inputs (Level 3) | Fuel swap contracts
Financial Assets:
Derivative asset, current		1
Derivative contracts	8
Carrying Value
Financial Assets:
Deferred compensation trust	12	13
Derivative asset, current	2
Net investment hedge	3
Total financial assets	18	19
Total financial liabilities	41	1
Carrying Value | Fuel swap contracts
Financial Assets:
Derivative asset, current		1
Derivative contracts	8
Carrying Value | Interest rate swap contracts
Financial Assets:
Derivative asset, current		5
Derivative contracts	$ 33	$ 1