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Goodwill and Intangible Assets (Narrative) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Goodwill [Line Items]      
Amortization expense for intangible assets $ 79 $ 69 $ 95
Acquisition of intangible assets $ 311    
Weighted-average amortization period (years) 7 years    
Virginia Electric and Power Company      
Goodwill [Line Items]      
Amortization expense for intangible assets $ 31 $ 28 $ 30
Acquisition of intangible assets $ 276    
Weighted-average amortization period (years) 7 years