Fair Value Measurements (Narrative) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets and other charges	$ 30,000,000	$ 98,000,000
Unrealized gains (losses) included in operating revenue in Level 3 fair value category	(8,000,000)
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains (losses) included in operating revenue in Level 3 fair value category		1,000,000
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
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		91,000,000
Asset impairment charges after tax		68,000,000
Virginia Electric and Power Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gains (losses) included in operating revenue in Level 3 fair value category	$ 0	$ 0