Fair Value Measurements (Assets and Liabilities that are Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		$ 1,209	$ 613
Derivative Liabilities		1,314	868
Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		404	300
Derivative Liabilities		508	470
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		8,406	8,161
Total Liabilities		1,314	868
Fair Value, Measurements, Recurring | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		3,792	3,847
Total Liabilities		508	470
Fair Value, Measurements, Recurring | Equity securities: | U.S.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	5,013	5,241
Fair Value, Measurements, Recurring | Equity securities: | U.S. | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	2,325	2,420
Fair Value, Measurements, Recurring | Fixed Income | Corporate debt instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	839	881
Fair Value, Measurements, Recurring | Fixed Income | Corporate debt instruments | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	509	531
Fair Value, Measurements, Recurring | Fixed Income | Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	1,360	1,455
Fair Value, Measurements, Recurring | Fixed Income | Government Securities | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	554	599
Fair Value, Measurements, Recurring | Cash equivalents and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and other	[1]	(15)	(29)
Fair Value, Measurements, Recurring | Cash equivalents and other | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and other	[2]		(3)
Fair Value, Measurements, Recurring | Foreign Currency Exchange Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		4	8
Fair Value, Measurements, Recurring | Foreign Currency Exchange Rate | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset			8
Derivative Liabilities		4
Fair Value, Measurements, Recurring | Commodity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		441	282
Derivative Liabilities		948	469
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		104	146
Derivative Liabilities		304	133
Fair Value, Measurements, Recurring | Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		768	323
Derivative Liabilities		362	399
Fair Value, Measurements, Recurring | Interest Rate | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		300	146
Derivative Liabilities		200	337
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		5,196	5,411
Fair Value, Measurements, Recurring | Level 1 | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		2,418	2,510
Fair Value, Measurements, Recurring | Level 1 | Equity securities: | U.S.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	5,013	5,241
Fair Value, Measurements, Recurring | Level 1 | Equity securities: | U.S. | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	2,325	2,420
Fair Value, Measurements, Recurring | Level 1 | Fixed Income | Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	198	199
Fair Value, Measurements, Recurring | Level 1 | Fixed Income | Government Securities | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	93	93
Fair Value, Measurements, Recurring | Level 1 | Cash equivalents and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and other	[1]	(15)	(29)
Fair Value, Measurements, Recurring | Level 1 | Cash equivalents and other | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents and other	[2]		(3)
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		3,001	2,520
Total Liabilities		1,307	860
Fair Value, Measurements, Recurring | Level 2 | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		1,345	1,227
Total Liabilities		501	462
Fair Value, Measurements, Recurring | Level 2 | Fixed Income | Corporate debt instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	839	881
Fair Value, Measurements, Recurring | Level 2 | Fixed Income | Corporate debt instruments | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	509	531
Fair Value, Measurements, Recurring | Level 2 | Fixed Income | Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[1]	1,162	1,256
Fair Value, Measurements, Recurring | Level 2 | Fixed Income | Government Securities | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	[2]	461	506
Fair Value, Measurements, Recurring | Level 2 | Foreign Currency Exchange Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		4	8
Fair Value, Measurements, Recurring | Level 2 | Foreign Currency Exchange Rate | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset			8
Derivative Liabilities		4
Fair Value, Measurements, Recurring | Level 2 | Commodity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		232	52
Derivative Liabilities		941	461
Fair Value, Measurements, Recurring | Level 2 | Commodity | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		75	36
Derivative Liabilities		297	125
Fair Value, Measurements, Recurring | Level 2 | Interest Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		768	323
Derivative Liabilities		362	399
Fair Value, Measurements, Recurring | Level 2 | Interest Rate | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		300	146
Derivative Liabilities		200	337
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		209	230
Total Liabilities		7	8
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		29	110
Total Liabilities		7	8
Fair Value, Measurements, Recurring | Level 3 | Commodity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		209	230
Derivative Liabilities		7	8
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset		29	110
Derivative Liabilities		$ 7	$ 8

[1] Includes investments held in the nuclear decommissioning and rabbi trusts. Excludes $361 million and $366 million of assets at March 31, 2022 and December 31, 2021, respectively, measured at fair value using NAV (or its equivalent) as a practical expedient which are not required to be categorized in the fair value hierarchy.

[2] Includes investments held in the nuclear decommissioning trusts. Excludes $194 million and $185 million of assets at March 31, 2022 and December 31, 2021, respectively, measured at fair value using NAV (or its equivalent) as a practical expedient which are not required to be categorized in the fair value hierarchy.