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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 360	$ 134	$ 86	$ 422
Total realized and unrealized gains (losses):
Included in earnings	14	(103)	(134)	(191)
Operating Revenue	$ 13	$ (10)	$ 7	$ (8)
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	$ (77)	$ (174)	$ 230	$ (463)
Settlements	(40)	103	54	174
Purchases	2	0	30	16
Ending balance	269	(49)	269	(49)
Virginia Electric and Power Company
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	105	(3)	(116)	221
Total realized and unrealized gains (losses):
Included in earnings	$ 10	$ (107)	$ (136)	$ (195)
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	$ (7)	$ (176)	$ 219	$ (400)
Settlements	(17)	107	103	179
Purchases	0	0	21	16
Ending balance	91	(179)	91	(179)
Discontinued operations
Total realized and unrealized gains (losses):
Included in earnings	$ (3)	$ 1	$ (4)	$ 1