Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Gain (Loss) Recognized in AOCI, After-Tax		$ (9)	$ 77	$ (3)
Less: Gain Reclassified to Income, After-Tax		37	(43)	35
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Balance as of Beginning of Year		0	3
Gain (Loss) Recognized in AOCI, Pre-Tax		(2)	0
Less: Gain Reclassified into Income, Pre-Tax		0	(3)
Balance as of End of Year		(2)	0	3
Balance as of Beginning of Year		0	2
Gain (Loss) Recognized in AOCI, After-Tax	$ (1)	(1)	0	2
Less: Gain Reclassified to Income, After-Tax		0	(2)	0
Balance as of End of Year		$ (1)	$ 0	$ 2