Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions		3 Months Ended
		Mar. 31, 2022 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2021 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 1,209	$ 613
Fair Value of Derivative Liabilities		1,314	868
Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		404	300
Fair Value of Derivative Liabilities		508	470
Fair Value, Measurements, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		8,406	8,161
Total liabilities		1,314	868
Fair Value, Measurements, Recurring | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		3,792	3,847
Total liabilities		508	470
Fair Value, Measurements, Recurring | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		441	282
Fair Value of Derivative Liabilities		948	469
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		104	146
Fair Value of Derivative Liabilities		304	133
Fair Value, Measurements, Recurring | Level 3
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		209	230
Total liabilities		7	8
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		29	110
Total liabilities		7	8
Fair Value, Measurements, Recurring | Level 3 | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		209	230
Fair Value of Derivative Liabilities		7	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		29	110
Fair Value of Derivative Liabilities		7	$ 8
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets	[1]	12
Fair Value of Derivative Liabilities	[1]	5
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 Assets	[1]	12
Fair Value of Derivative Liabilities	[1]	$ 5
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Minimum [Member] | 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 | Natural Gas | Minimum [Member] | 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 | Natural Gas | Minimum [Member] | Liabilities | 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 | Natural Gas | Minimum [Member] | Liabilities | 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 | Natural Gas | Maximum | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1],[2]	6
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Natural Gas | Maximum | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1],[2]	6
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	[1],[2]	5
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	[1],[2]	5
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | 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 | 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 | Natural Gas | Weighted Average | Liabilities | 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 | 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]	(1)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 17
Fair Value of Derivative Liabilities		2
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		17
Fair Value of Derivative Liabilities		$ 2
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum [Member] | Assets | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	(1)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum [Member] | Assets | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	(1)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum [Member] | Liabilities | Market Price
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	(3)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum [Member] | Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MWh	[2]	(3)
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]	7
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]	7
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]	3
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]	3
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],[3]	2
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],[3]	2
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],[3]	1
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],[3]	1
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Electricity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 180
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | Electricity | Minimum [Member] | 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]	85
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],[3]	47

[1] Includes basis.

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

[3] Averages weighted by volume.