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Financial Risk Management Activities (Schedule Of Derivative Instruments Designated As Cash Flow Hedges) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Pre-Tax Gain (Loss) attributed to Cash Flow Hedges Recognized in AOCI on Derivatives (Effective Portion) $ (23) $ (2) $ 0
Amount of Pre-Tax Loss Reclassified from AOCL into Income, Effective Portion (4)    
Amount of Pre-Tax Gain Reclassified from AOCI into Income, Effective Portion   0 3
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) (23) (2) 0
Amount of Pre-Tax Loss Reclassified from AOCL into Income, Effective Portion (4)    
Amount of Pre-Tax Gain Reclassified from AOCI into Income, Effective Portion   $ 0 3
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 (3)   2
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 $ (3)   $ 2