Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 8	$ (7)	$ 21	$ (23)
(Gain) Loss into Income	1	8	5	18
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period			(2)	0	$ 0
Gain (Loss) in AOCI			(24)		(2)
(Gain) Loss into Income	1		1		0
Pre-Tax Balance at End of Period	(25)		(25)		(2)
After-Tax Balance at Beginning of Period			(1)	0	0
Gain (Loss) in AOCI	(13)	(1)	(17)	(1)	(1)
(Gain) Loss into Income	0	$ 0	0	$ 0	0
After-Tax Balance at End of Period	$ (18)		$ (18)		$ (1)