Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2021 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2020 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		$ 613	$ 397
Fair Value of Derivative Liabilities		868	486
Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		300	181
Fair Value of Derivative Liabilities		470	405
Fair Value, Measurements, Recurring
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		8,161	6,959
Total liabilities		868	486
Fair Value, Measurements, Recurring | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		3,847	3,223
Total liabilities		470	405
Fair Value, Measurements, Recurring | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		282	167
Fair Value of Derivative Liabilities		469	55
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		146	115
Fair Value of Derivative Liabilities		133	29
Fair Value, Measurements, Recurring | Level 3
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		230	110
Total liabilities		8	7
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Total assets		110	110
Total liabilities		8	7
Fair Value, Measurements, Recurring | Level 3 | Commodity
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		230	110
Fair Value of Derivative Liabilities		8	7
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Assets		110	110
Fair Value of Derivative Liabilities		8	$ 7
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]	54
Fair Value of Derivative Liabilities	[1]	3
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]	54
Fair Value of Derivative Liabilities	[1]	$ 3
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | 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 | 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 | Natural Gas | Minimum | Derivative Financial Instruments, 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 | Derivative Financial Instruments, 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]	8
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 | Derivative Financial Instruments, Liabilities | 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 | Natural Gas | Maximum | Derivative Financial Instruments, Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[1],[2]	4
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 | Derivative Financial Instruments, 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 | Derivative Financial Instruments, 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		$ 51
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		51
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]	(2)
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]	(2)
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Minimum | Derivative Financial Instruments, 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 | Derivative Financial Instruments, 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]	11
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]	11
Fair Value, Measurements, Recurring | Level 3 | Discounted Cash Flow | Commodity | FTRs | Maximum | Derivative Financial Instruments, 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 | FTRs | Maximum | Derivative Financial Instruments, 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 | 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 | Derivative Financial Instruments, 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 | Derivative Financial Instruments, 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		$ 120
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]	28
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]	72
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]	43
Fair Value, Measurements, Recurring | Level 3 | Option Model | Commodity | Natural Gas
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of Derivative Liabilities		$ 5
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		$ 5
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]	3
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)	[4]	19.00%
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]	9
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)	[4]	27.00%
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],[3]	6
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]	24.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Physical Options | Natural Gas | Minimum | Derivative Financial Instruments, Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	3
Fair Value, Measurements, Recurring | Level 3 | Option Model | Physical Options | Natural Gas | Minimum | Derivative Financial Instruments, Liabilities | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[4]	19.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Physical Options | Natural Gas | Maximum | Derivative Financial Instruments, Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2]	9
Fair Value, Measurements, Recurring | Level 3 | Option Model | Physical Options | Natural Gas | Maximum | Derivative Financial Instruments, Liabilities | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[4]	27.00%
Fair Value, Measurements, Recurring | Level 3 | Option Model | Physical Options | Natural Gas | Weighted Average | Derivative Financial Instruments, Liabilities | Market Price | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Market Price | $ / MMBTU	[2],[3]	6
Fair Value, Measurements, Recurring | Level 3 | Option Model | Physical Options | Natural Gas | Weighted Average | Derivative Financial Instruments, Liabilities | Price Volatility | Virginia Electric and Power Company
Fair Value, Option, Quantitative Disclosures [Line Items]
Price volatility (percentage)	[3],[4]	24.00%

[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.