Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions		9 Months Ended
		Sep. 30, 2022 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2021 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 2,469	$ 613
Fair Value of Derivative Liabilities		2,371	868
Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		961	300
Fair Value of Derivative Liabilities		917	470
Fair Value, Measurements, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		7,772	8,161
Total liabilities		2,371	868
Fair Value, Measurements, Recurring | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		3,809	3,847
Total liabilities		917	470
Fair Value, Measurements, Recurring | Commodity Contract
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		870	282
Fair Value of Derivative Liabilities		1,509	469
Fair Value, Measurements, Recurring | Commodity Contract | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		359	146
Fair Value of Derivative Liabilities		503	133
Fair Value, Measurements, Recurring | Level 3
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		499	230
Total liabilities		17	8
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		288	110
Total liabilities		17	8
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		499	230
Fair Value of Derivative Liabilities		17	8
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		288	110
Fair Value of Derivative Liabilities		$ 17	$ 8
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract | Natural Gas | Minimum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[1]	(2)
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract | Natural Gas | Maximum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[1]	6
Fair Value, Measurements, Recurring | Level 3 | Commodity Contract | Natural Gas | Weighted Average | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[1],[2]	(1)
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	[1]	$ 1
Fair Value of Derivative Liabilities	[1]	12
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	[1]	1
Fair Value of Derivative Liabilities	[1]	$ 12
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1]	(2)
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Minimum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[3]	(2)
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Minimum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[3]	(2)
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1]	6
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Maximum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[3]	8
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Maximum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[3]	5
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1],[2]	(1)
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[3]	1
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Natural Gas | Weighted Average | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[3]	1
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 263
Fair Value of Derivative Liabilities		5
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		263
Fair Value of Derivative Liabilities		$ 5
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Minimum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	1
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Minimum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	1
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Minimum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	1
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Minimum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	1
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Maximum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	19
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Maximum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	19
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Maximum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	10
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Maximum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	10
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Weighted Average | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[3]	5
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | 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]	5
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | FTRs | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[3]	4
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | 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]	4
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Electricity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 211
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Electricity | Minimum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	28
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Electricity | Maximum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[3]	199
Fair Value, Measurements, Recurring | Level 3 | Valuation, Income Approach | Commodity Contract | Electricity | Weighted Average | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[3]	51
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities	[1]	$ 24
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity Contract | Natural Gas | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities	[1]	$ 24
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	[3]	4
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)	[4]	13.00%
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	[3]	17
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)	[4]	70.00%
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	[2],[3]	10
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)	[2],[4]	51.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Minimum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[3]	4
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Minimum | Assets | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[4]	8.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Maximum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[3]	19
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Maximum | Assets | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[4]	31.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Weighted Average | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[3]	10
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Weighted Average | Assets | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[2],[4]	51.00%

[1] Includes basis.

[2] Averages weighted by volume.

[3] Represents market prices beyond defined terms for Levels 1 and 2.

[4] Represents volatilities unrepresented in published markets.