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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) in AOCI	$ (4)	$ 3	$ (28)	$ 43
(Gain) Loss into Income	(2)	0	(8)	6
Cash Flow Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-Tax Balance at Beginning of Period			(13)	(21)	$ (21)
Gain (Loss) in AOCI			0		(6)
(Gain) Loss into Income	1	5	3	11	14
Pre-Tax Balance at End of Period	(10)		(10)		(13)
After-Tax Balance at Beginning of Period			(9)	(15)	(15)
Gain (Loss) in AOCI	0	0	0	(4)	(4)
(Gain) Loss into Income	(1)	$ (4)	(2)	$ (8)	(10)
After-Tax Balance at End of Period	$ (7)		$ (7)		$ (9)