Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Gain (Loss) Recognized in AOCI, After-Tax	$ (3)	$ (30)	$ (135)
Less: Gain Reclassified to Income, After-Tax	35	18	(53)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Balance as of Beginning of Year	0	17
Gain (Loss) Recognized in AOCI, Pre-Tax	3	3
Less: Gain Reclassified into Income, Pre-Tax	0	(20)	9
Balance as of End of Year	3	0	17
Balance as of Beginning of Year	0	10
Gain (Loss) Recognized in AOCI, After-Tax	2	2	7
Less: Gain Reclassified to Income, After-Tax	0	(12)	5
Balance as of End of Year	$ 2	$ 0	$ 10