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Acquisitions and Dispositions (Business Review Dispositions) (Narrative) (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
 [1]
Mar. 31, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Dec. 31, 2023
Apr. 30, 2024
Sep. 30, 2023
Business Acquisition And Dispositions [Line Items]                  
Income tax expense (benefit) $ 216.0 [1] $ 213.0   $ 476.0 [2] $ 421.0 [2]        
Deferred income tax expense (benefit)       455.0 $ (281.0)        
East Ohio | Enbridge                  
Business Acquisition And Dispositions [Line Items]                  
Disposal group, total value of consideration                 $ 6,600.0
Disposal group, cash consideration                 4,300.0
Disposal group, indebtedness                 2,300.0
Disposal group, recognized a pre-tax gain (loss)     $ (97.0)            
Disposal group, gain (loss) recorded after tax     (109.0)            
Goodwill write-off     1,500.0            
Deferred income tax expense (benefit)             $ 29.0    
Questar Gas and Wexpro | Enbridge                  
Business Acquisition And Dispositions [Line Items]                  
Disposal group, total value of consideration                 4,300.0
Disposal group, cash consideration                 3,000.0
Disposal group, indebtedness                 1,300.0
Disposal group, recognized a pre-tax gain (loss) (8.0)   78.0       236.0    
Disposal group, gain (loss) recorded after tax $ 34.0   78.0       231.0    
Goodwill write-off           $ 700.0      
Income tax expense (benefit)     (5.0)            
Deferred income tax expense (benefit)     $ (10.0)       472.0    
PSNC | Enbridge                  
Business Acquisition And Dispositions [Line Items]                  
Disposal group, total value of consideration                 3,300.0
Disposal group, cash consideration                 2,000.0
Disposal group, indebtedness                 $ 1,300.0
Disposal group, recognized a pre-tax gain (loss)       (34.0)          
Disposal group, gain (loss) recorded after tax       (30.0)          
Goodwill write-off       $ 0.7          
Deferred income tax expense (benefit)             $ 334.0    
Deferred tax of classified held for sale           $ 16.0      
Other Sales | Birdseye and Madison                  
Business Acquisition And Dispositions [Line Items]                  
Disposal group, cash consideration               $ 17.0  
[1] The significant expense categories and amounts in the segment information presented above align with the segment-level information that is regularly provided to Dominion Energy’s CODM.
[2] The significant expense categories and amounts in the segment information presented above align with the segment-level information that is regularly provided to Dominion Energy’s CODM.