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Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail)
$ in Millions
 9 Months Ended
Sep. 30, 2025
USD ($)
$ / MMBTU
$ / MWh
Dec. 31, 2024
USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets $ 750 $ 1,399
Fair Value of Derivative Liabilities 267 512
Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets 304 375
Fair Value of Derivative Liabilities 90 225
Fair Value, Measurements, Recurring    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Total assets 9,532 9,259
Total liabilities 267 512
Fair Value, Measurements, Recurring | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Total assets 4,970 4,563
Total liabilities 90 225
Fair Value, Measurements, Recurring | Commodity Contract    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets 528 494
Fair Value of Derivative Liabilities 143 123
Fair Value, Measurements, Recurring | Commodity Contract | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets 195 115
Fair Value of Derivative Liabilities 25 33
Fair Value, Measurements, Recurring | Level 3    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Total assets 446 399
Total liabilities 35 15
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Total assets 168 70
Total liabilities 0 2
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets 446 399
Fair Value of Derivative Liabilities 35 15
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets 168 70
Fair Value of Derivative Liabilities 0 $ 2
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Total assets 446  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Total assets 168  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [1],[2] 41  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [1],[2] $ 41  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Minimum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] (2)  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Minimum | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] (2)  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Maximum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] 4  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Maximum | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] 2  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Weighted Average | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2],[3] (1)  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Natural Gas | Weighted Average | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2],[3] (1)  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [2] $ 119  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [2] $ 119  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Minimum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] (4)  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Minimum | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] (4)  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Maximum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] 15  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Maximum | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] 15  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Weighted Average | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2],[3] 7  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Weighted Average | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [3] 7  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [2] $ 230  
Fair Value of Derivative Liabilities [2] $ 35  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Minimum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] 30  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Minimum | Liabilities | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] 30  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Maximum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] 116  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Maximum | Liabilities | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2] 123  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Weighted Average | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2],[3] 54  
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Weighted Average | Liabilities | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MWh [2],[3] 66  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [1],[2] $ 56  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Fair Value of Derivative Assets [1],[2] $ 8  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Minimum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] 1  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Minimum | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] 3  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Minimum | Assets | Price Volatility    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Price volatility (percentage) [1],[4] 11.00%  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Minimum | Assets | Price Volatility | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Price volatility (percentage) [1],[4] 14.00%  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Maximum | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] 9  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Maximum | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2] 8  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Maximum | Assets | Price Volatility    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Price volatility (percentage) [1],[4] 73.00%  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Maximum | Assets | Price Volatility | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Price volatility (percentage) [1],[4] 71.00%  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Assets | Market Price    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2],[3] 4  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Assets | Market Price | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Market Price | $ / MMBTU [1],[2],[3] 5  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Assets | Price Volatility    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Price volatility (percentage) [1],[3],[4] 44.00%  
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Assets | Price Volatility | Virginia Electric and Power Company    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Price volatility (percentage) [1],[3],[4] 41.00%  
[1] Includes basis.
[2] Represents market prices beyond defined terms for Levels 1 and 2.
[3] Averages weighted by volume.
[4] Represents volatilities unrepresented in published markets.