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, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 134	$ 480	$ 422	$ 222
Total realized and unrealized gains (losses):
Included in earnings	$ (103)	$ 181	$ (191)	$ 346
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Electric fuel and other energy-related purchases	Electric fuel and other energy-related purchases	Electric fuel and other energy-related purchases	Electric fuel and other energy-related purchases
Included in regulatory assets/liabilities	$ (174)	$ 2	$ (463)	$ 243
Settlements	103	(181)	174	(346)
Purchases			16	17
Ending balance	(49)	482	(49)	482
Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	(3)	245	221	102
Total realized and unrealized gains (losses):
Included in earnings	$ (107)	$ 142	$ (195)	$ 293
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Electric fuel and other energy-related purchases	Electric fuel and other energy-related purchases	Electric fuel and other energy-related purchases	Electric fuel and other energy-related purchases
Included in regulatory assets/liabilities	$ (176)	$ 26	$ (400)	$ 152
Settlements	107	(142)	179	(293)
Purchases			16	17
Ending balance	(179)	$ 271	(179)	$ 271
Discontinued operations
Total realized and unrealized gains (losses):
Included in earnings	1		1
Operating Revenue
Total realized and unrealized gains (losses):
Operating Revenue	$ (10)		$ (8)