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Financial Risk Management Activities (Schedule Of Reconciliation For Derivative Activity Included In Accumulated Other Comprehensive Loss) (Detail) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]      
Gain (Loss) in AOCI $ (40) $ 10  
(Gain) Loss into Income (2) 2  
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 2 14
Pre-Tax Balance at End of Period (12)   (13)
After-Tax Balance at Beginning of Period (9) (15) (15)
Gain (Loss) in AOCI 0 (4) (4)
(Gain) Loss into Income (1) $ (1) (10)
After-Tax Balance at End of Period $ (8)   $ (9)