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Significant Accounting Policies (Narrative) (Detail)
$ / shares in Units, $ in Millions
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2020
USD ($)
Mar. 31, 2019
Facility
MW
Jan. 31, 2019
USD ($)
Jun. 30, 2020
USD ($)
$ / shares
Jun. 30, 2019
USD ($)
Mar. 31, 2019
USD ($)
Jun. 30, 2020
USD ($)
$ / shares
Jun. 30, 2019
USD ($)
Dec. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
Significant Accounting Policies [Line Items]                    
Impairment of assets and other charges       $ 531 $ 312   $ 1,299 $ 1,147    
Increase to nuclear decommissioning asset retirement obligation       89            
Property, plant and equipment       $ 67,980     $ 67,980     $ 69,082 [1]
Change In Depreciation Rates From New Depreciation Study                    
Significant Accounting Policies [Line Items]                    
Increase in EPS | $ / shares       $ 0.01     $ 0.01      
Change In Depreciation Rates From New Depreciation Study | Merchant generation assets | Scenario Forecast                    
Significant Accounting Policies [Line Items]                    
Increase in EPS | $ / shares                 $ 0.03  
Dominion Energy Gas Holdings, LLC                    
Significant Accounting Policies [Line Items]                    
Impairment of assets and other charges       $ 482 13   $ 482 13    
Property, plant and equipment       11,204     11,204     11,628 [2]
Virginia Electric and Power Company                    
Significant Accounting Policies [Line Items]                    
Impairment of assets and other charges       44 197   808 $ 743    
MW Capacity | MW   1,292                
Number of facilities in cold reserve units retired | Facility   6                
Asset retirement obligations       91     91     340 [3]
Property, plant and equipment       31,499     31,499     $ 32,882 [3]
Virginia Electric and Power Company | Change In Depreciation Rates From New Depreciation Study                    
Significant Accounting Policies [Line Items]                    
Increase (decrease) in depreciation expense       (8)     (16)      
Increase (decrease) in depreciation expense, after tax       (6)     (12)      
Virginia Electric and Power Company | Change In Depreciation Rates From New Depreciation Study | Merchant generation assets | Scenario Forecast                    
Significant Accounting Policies [Line Items]                    
Increase (decrease) in depreciation expense                 $ (31)  
Increase (decrease) in depreciation expense, after tax                 $ (23)  
Virginia Electric and Power Company | Electric Generation Facilities                    
Significant Accounting Policies [Line Items]                    
Charges recorded with dismantling       30            
Charges recorded with dismantling after tax       22            
Virginia Electric and Power Company | Impairment of Assets and Other Charges                    
Significant Accounting Policies [Line Items]                    
Impairment of assets and other charges $ 754   $ 160   62 $ 369        
Asset impairment charges after tax $ 561   $ 119   $ 46 $ 275        
DETI                    
Significant Accounting Policies [Line Items]                    
Impairment of assets and other charges             482      
Asset impairment charges after tax             359      
Asset retirement obligations       75     75      
Property, plant and equipment       $ 40     $ 40      
Dominion Energy Midstream Partners, LP | Terra Nova Renewable Partners | Merchant Solar Projects | Call Option                    
Significant Accounting Policies [Line Items]                    
Percentage ownership in total units       67.00%     67.00%      
Cove Point                    
Significant Accounting Policies [Line Items]                    
Percentage ownership in total units                   75.00%
Cove Point | Dominion Energy Gas Holdings, LLC                    
Significant Accounting Policies [Line Items]                    
Percentage of equity interest sold to noncontrolling interest owners       25.00%     25.00%      
Four Brothers and Three Cedars                    
Significant Accounting Policies [Line Items]                    
Business Acquisition, Percentage of Voting Interests Acquired       50.00%     50.00%      
Four Brothers and Three Cedars | Dominion Energy Midstream Partners, LP | Terra Nova Renewable Partners | Merchant Solar Projects                    
Significant Accounting Policies [Line Items]                    
Percentage of equity interest sold to noncontrolling interest owners       33.00%     33.00%      
[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.
[2] Dominion Energy Gas’ Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.
[3] Virginia Power’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.