Fair Value Measurements (Narrative) (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets and other charges									$ 307,000,000		$ 1,401,000,000		$ 194,000,000
Net Income (Loss) From Discontinued Operations	$ (71,000,000)	$ (541,000,000)	$ 168,000,000	$ 281,000,000	$ 122,000,000	$ 150,000,000	$ 212,000,000	$ 410,000,000	(163,000,000)	[1],[2]	894,000,000	[1],[2]	1,358,000,000	[1],[2]
Net Income (Loss) From Discontinued Operations, after tax									(163,000,000)		894,000,000		1,358,000,000
Unrealized gains or losses included in earnings in Level 3 fair value category									7,000,000		0		0
Level 3 | Corporate Office Building
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets, estimated fair value	35,000,000								35,000,000				26,000,000
Impairment of Assets and Other Charges | Corporate Office Building
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets and other charges									93,000,000				16,000,000
Asset impairment charges after tax									69,000,000				12,000,000
Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains or losses included in earnings in Level 3 fair value category									0		$ 0		0
Virginia Electric and Power Company | Level 2 | Maximum | Nonregulated Retail Software Development
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets, estimated fair value													1,000,000
Virginia Electric and Power Company | Impairment of Assets and Other Charges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets and other charges							191,000,000
Asset impairment charges after tax							$ 142,000,000
Virginia Electric and Power Company | Impairment of Assets and Other Charges | Nonregulated Retail Software Development
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets and other charges													20,000,000
Asset impairment charges after tax													$ 15,000,000
Nonregulated Solar Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Income (Loss) From Discontinued Operations									15,000,000
Net Income (Loss) From Discontinued Operations, after tax									11,000,000
Nonregulated Solar Assets | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets, estimated fair value	$ 22,000,000								$ 22,000,000

[1] Includes income tax expense of $1.3 billion, $197 million and $374 million for the years ended December 31, 2023, 2022 and 2021, respectively.

[2] See Note 9 for amounts attributable to related parties.