Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category) (Detail) - Commodity - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 480	$ 62	$ 222	$ 103
Total realized and unrealized gains (losses):
Included in earnings		(6)		(8)
Included in earnings	$ 181	$ 29	$ 346	$ 12
Revenue, Product and Service [Extensible Enumeration]	us-gaap:RegulatedOperatingRevenueElectricNonNuclear	us-gaap:RegulatedOperatingRevenueElectricNonNuclear	us-gaap:RegulatedOperatingRevenueElectricNonNuclear	us-gaap:RegulatedOperatingRevenueElectricNonNuclear
Included in regulatory assets/liabilities	$ 2	$ 88	$ 243	$ 49
Settlements	(181)	(29)	(346)	(12)
Purchases			17
Ending balance	482	144	482	144
Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	245	74	102	103
Total realized and unrealized gains (losses):
Included in earnings	$ 142	$ 27	$ 293	$ 10
Revenue, Product and Service [Extensible Enumeration]	us-gaap:RegulatedOperatingRevenueElectricNonNuclear	us-gaap:RegulatedOperatingRevenueElectricNonNuclear	us-gaap:RegulatedOperatingRevenueElectricNonNuclear	us-gaap:RegulatedOperatingRevenueElectricNonNuclear
Included in regulatory assets/liabilities	$ 26	$ 41	$ 152	$ 12
Settlements	(142)	(27)	(293)	(10)
Purchases	0	0	17	0
Ending balance	$ 271	$ 115	$ 271	$ 115