Fair Value Measurements (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Deferred compensation plan assets	$ 92	$ 95
Total assets	99	106
Liabilities:
Total liabilities	387	255
Total recurring fair value measurements	(288)	(149)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Deferred compensation plan assets	92	95
Total assets	92	95
Liabilities:
Total liabilities	0	0
Total recurring fair value measurements	92	95
Significant Other Observable Inputs (Level 2)
Assets:
Deferred compensation plan assets	0	0
Total assets	7	11
Liabilities:
Total liabilities	387	255
Total recurring fair value measurements	(380)	(244)
Significant Unobservable Inputs (Level 3)
Assets:
Deferred compensation plan assets	0	0
Total assets	0	0
Liabilities:
Total liabilities	0	0
Total recurring fair value measurements	0	0
Commodity derivatives
Assets:
Derivative assets	7	11
Liabilities:
Commodity derivatives	387	255
Commodity derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Derivative assets	0	0
Liabilities:
Commodity derivatives	0	0
Commodity derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivative assets	7	11
Liabilities:
Commodity derivatives	387	255
Commodity derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivative assets	0	0
Liabilities:
Commodity derivatives	$ 0	$ 0