Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ (7)	$ (6)	$ 14	$ (29)
(Gain) Loss into Income	1	9	6	27
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		2		0
Pre-Tax Balance at End of Period	(24)		(24)		(2)
After-Tax Balance at Beginning of Period			(1)	0	0
Gain (Loss) in AOCI	0	0	(17)	(1)	(1)
(Gain) Loss into Income	1	$ 0	1	$ 0	0
After-Tax Balance at End of Period	$ (17)		$ (17)		$ (1)