Related-Party Transactions (Narrative) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Derivative Asset	$ 656,000,000		$ 656,000,000		$ 397,000,000
Derivative Liabilities	950,000,000		950,000,000		486,000,000
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Derivative Asset	359,000,000		359,000,000		181,000,000
Derivative Liabilities	453,000,000		453,000,000		405,000,000
Payable to affiliates	310,000,000		310,000,000		380,000,000	[1]
Outstanding borrowings, net of repayments, under money pool for non-regulated subsidiaries	$ 0		$ 0		0
Issuance of common stock to Dominion	0	0	0	0
Virginia Electric and Power Company | Pension Benefits | Amounts Associated With Dominion Pension Plan
Related Party Transaction [Line Items]
Amounts due to Dominion, noncurrent	$ 500,000,000		$ 500,000,000		436,000,000
Virginia Electric and Power Company | Medical Coverage for Local retirees | Amounts Associated with the Dominion Retiree Health and Welfare Plan
Related Party Transaction [Line Items]
Amounts due from Dominion, noncurrent	412,000,000		412,000,000		354,000,000
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Derivative Asset	63,000,000		63,000,000		3,000,000
Derivative Liabilities	2,000,000		2,000,000		22,000,000
Virginia Electric and Power Company | Principal Owner | Short-Term Borrowing Arrangements
Related Party Transaction [Line Items]
Payable to affiliates	$ 310,000,000		$ 310,000,000		$ 380,000,000

[1] Virginia Power’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.