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, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Gain (Loss) Recognized in AOCI, After-Tax	$ (38)	$ (9)	$ 77
Less: Gain Reclassified to Income, After-Tax	7	37	(43)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Balance as of Beginning of Year	(2)	0
Gain (Loss) Recognized in AOCI, Pre-Tax	(23)	(2)
Less: Gain Reclassified into Income, Pre-Tax	4	0	(3)
Balance as of End of Year	(21)	(2)	0
Balance as of Beginning of Year	(1)	0
Gain (Loss) Recognized in AOCI, After-Tax	(17)	(1)	0
Less: Gain Reclassified to Income, After-Tax	3	0	(2)
Balance as of End of Year	$ (15)	$ (1)	$ 0