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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ 3	$ (7)	$ 43	$ 14
(Gain) Loss into Income	0	(1)	6	(6)
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period			(21)	(2)	$ (2)
Gain (Loss) in AOCI			(6)		(23)
(Gain) Loss into Income	5	1	11	2	4
Pre-Tax Balance at End of Period	(16)		(16)		(21)
After-Tax Balance at Beginning of Period			(15)	(1)	(1)
Gain (Loss) in AOCI	0	0	(4)	(17)	(17)
(Gain) Loss into Income	(4)	$ (1)	(8)	$ (1)	(3)
After-Tax Balance at End of Period	$ (11)		$ (11)		$ (15)