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
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 13	$ (16)
(Gain) Loss into Income	4	10
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	(5)		(2)
(Gain) Loss into Income	0		0
Pre-Tax Balance at End of Period	(7)		(2)
After-Tax Balance at Beginning of Period	(1)	0	0
Gain (Loss) in AOCI	(4)	0	(1)
(Gain) Loss into Income	0	$ 0	0
After-Tax Balance at End of Period	$ (5)		$ (1)