Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions		6 Months Ended
		Jun. 30, 2022 USD ($) $ / MWh $ / MMBTU	Dec. 31, 2021 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 2,110	$ 613
Fair Value of Derivative Liabilities		1,650	868
Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		791	300
Fair Value of Derivative Liabilities		585	470
Fair Value, Measurements, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		7,674	8,161
Total liabilities		1,650	868
Fair Value, Measurements, Recurring | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		3,775	3,847
Total liabilities		585	470
Fair Value, Measurements, Recurring | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		765	282
Fair Value of Derivative Liabilities		1,204	469
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		347	146
Fair Value of Derivative Liabilities		404	133
Fair Value, Measurements, Recurring | Level 3
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		502	230
Total liabilities		22	8
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		267	110
Total liabilities		22	8
Fair Value, Measurements, Recurring | Level 3 | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		502	230
Fair Value of Derivative Liabilities		22	8
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		267	110
Fair Value of Derivative Liabilities		22	$ 8
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities	[1]	32
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities	[1]	$ 32
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Minimum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	4
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Minimum | Assets | Price Volatility
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[3]	8.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Maximum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	19
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Maximum | Assets | Price Volatility
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[3]	31.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Weighted Average | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[4]	9
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas | Weighted Average | Assets | Price Volatility
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[3],[4]	22.00%
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	[2]	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)	[3]	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	[2]	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)	[3]	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],[4]	9
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)	[3],[4]	22.00%
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities	[1]	$ 17
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities	[1]	$ 17
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Minimum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	(2)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Minimum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	(2)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Maximum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	6
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Maximum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	6
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[4]	(1)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Weighted Average | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[4]	(1)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 235
Fair Value of Derivative Liabilities		5
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		235
Fair Value of Derivative Liabilities		$ 5
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	0
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	0
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	0
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	0
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Maximum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	16
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Maximum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	16
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Maximum | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	11
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Maximum | Liabilities | 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 | FTRs | Weighted Average | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[4]	4
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Weighted Average | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[4]	4
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Weighted Average | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[4]	3
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Weighted Average | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[4]	3
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Electricity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 235
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | 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 | Electricity | Maximum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	141
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Electricity | Weighted Average | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2],[4]	52

[1] Includes basis.

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

[3] Represents volatilities unrepresented in published markets.

[4] Averages weighted by volume.