Related-Party Transactions (Narrative) (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Derivative Asset	$ 616,000,000		$ 616,000,000		$ 397,000,000
Derivative Liabilities	574,000,000		574,000,000		486,000,000
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Derivative Asset	283,000,000		283,000,000		181,000,000
Derivative Liabilities	335,000,000		335,000,000		405,000,000
Payable to affiliates	348,000,000		348,000,000		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	$ 479,000,000		$ 479,000,000		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	392,000,000		392,000,000		354,000,000
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Derivative Asset	26,000,000		26,000,000		3,000,000
Derivative Liabilities	1,000,000		1,000,000		22,000,000
Virginia Electric and Power Company | Principal Owner | Short-Term Borrowing Arrangements
Related Party Transaction [Line Items]
Payable to affiliates	$ 348,000,000		$ 348,000,000		$ 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.