Financial Risk Management Activities (Schedule Of Derivative Instruments Designated As Cash Flow Hedges) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pre-Tax Gain (Loss) attributed to Cash Flow Hedges Recognized in AOCI on Derivatives (Effective Portion)	$ (6)	$ (23)	$ (2)
Amount of Pre-Tax Loss Reclassified from AOCL into Income, Effective Portion	(14)	(4)	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(4)	7	37
Interest Expense [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pre-Tax Gain (Loss) attributed to Cash Flow Hedges Recognized in AOCI on Derivatives (Effective Portion)	(6)	(23)	(2)
Amount of Pre-Tax Loss Reclassified from AOCL into Income, Effective Portion	(14)	(4)	0
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount Reclassified from AOCI for Cash Flow Hedges, After-Tax	(10)	(3)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	10	3	$ 0
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount Reclassified from AOCI for Cash Flow Hedges, After-Tax	$ (10)	$ (3)