Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions		9 Months Ended
		Sep. 30, 2024 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2023 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 1,160	$ 1,350
Fair Value of Derivative Liabilities		181	697
Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		199	298
Fair Value of Derivative Liabilities		112	316
Fair Value, Measurements, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		8,959	7,865
Total liabilities		181	697
Fair Value, Measurements, Recurring | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		4,378	3,770
Total liabilities		112	316
Fair Value, Measurements, Recurring | Commodity Contract
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		109	550
Fair Value of Derivative Liabilities		450	299
Fair Value, Measurements, Recurring | Commodity Contract | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		60	117
Fair Value of Derivative Liabilities		146	232
Fair Value, Measurements, Recurring | Level 3
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		282	225
Total liabilities		13	139
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		93	21
Total liabilities		2	137
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		13	225
Fair Value of Derivative Liabilities		282	139
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		2	21
Fair Value of Derivative Liabilities		93	$ 137
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]	8
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]	$ 8
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]	3
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]	$ 72
Fair Value of Derivative Liabilities	[2]	1
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]	72
Fair Value of Derivative Liabilities	[2]	$ 1
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 | Minimum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	(6)
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Minimum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	(6)
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]	11
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]	11
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Maximum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	7
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Maximum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	7
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]	4
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	[2],[3]	4
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[3]	1
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | FTRs | Weighted Average | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[3]	1
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]	$ 186
Fair Value of Derivative Liabilities	[2]	$ 11
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]	27
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Minimum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	35
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]	118
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Maximum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	118
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]	48
Fair Value, Measurements, Recurring | Level 3 | Discounted cash flow | Commodity Contract | Electricity | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[3]	62
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]	$ 16
Fair Value of Derivative Liabilities	[1],[2]	1
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]	13
Fair Value of Derivative Liabilities	[1],[2]	$ 1
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]	1
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]	10.00%
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 | Minimum | Liabilities | 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 | Liabilities | Market Price | Virginia Electric and Power Company
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 | Liabilities | Price Volatility
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[1],[4]	44.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Minimum | Liabilities | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[1],[4]	44.00%
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]	5
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]	5
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]	71.00%
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 | Maximum | Liabilities | Market Price
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 | Maximum | Liabilities | 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 | Maximum | Liabilities | Price Volatility
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[1],[4]	54.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Maximum | Liabilities | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[1],[4]	54.00%
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]	3
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]	3
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]	46.00%
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]	52.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1],[2],[3]	2
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1],[2],[3]	2
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Liabilities | Price Volatility
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[1],[3],[4]	50.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Weighted Average | Liabilities | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[1],[3],[4]	50.00%

[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.