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		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 202	$ 56	$ 222	$ 103
Total realized and unrealized gains (losses):
Included in regulatory assets/liabilities	261	8	241	(39)
Settlements	(117)	(4)	(165)	17
Purchases	17		17
Ending balance	480	62	480	62
Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	22	56	102	103
Total realized and unrealized gains (losses):
Included in regulatory assets/liabilities	206	18	126	(29)
Settlements	(106)	(4)	(151)	17
Purchases	17	0	17	0
Ending balance	245	74	245	74
Operating Revenue
Total realized and unrealized gains (losses):
Included in earnings		(2)		(2)
Electric Fuel and Other Energy-Related Purchases
Total realized and unrealized gains (losses):
Included in earnings	117	4	165	(17)
Electric Fuel and Other Energy-Related Purchases | Virginia Electric and Power Company
Total realized and unrealized gains (losses):
Included in earnings	$ 106	$ 4	$ 151	$ (17)