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, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Gain (Loss) Recognized in AOCI, After-Tax	$ (11)	$ (38)	$ (9)
Less: Gain Reclassified to Income, After-Tax	(4)	7	37
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Balance as of Beginning of Year	(21)	(2)
Gain (Loss) Recognized in AOCI, Pre-Tax	(6)	(23)
Less: Gain Reclassified into Income, Pre-Tax	14	4
Balance as of End of Year	(13)	(21)	(2)
Balance as of Beginning of Year	(15)	(1)
Gain (Loss) Recognized in AOCI, After-Tax	(4)	(17)	(1)
Less: Gain Reclassified to Income, After-Tax	10	3	0
Balance as of End of Year	$ (9)	$ (15)	$ (1)