Related-Party Transactions (Narrative) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Derivative Asset	$ 849,000,000		$ 397,000,000
Derivative Liabilities	264,000,000		486,000,000
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Derivative Asset	359,000,000		181,000,000
Derivative Liabilities	178,000,000		405,000,000
Payable to affiliates	177,000,000		380,000,000	[1]
Outstanding borrowings, net of repayments, under money pool for non-regulated subsidiaries	$ 0		0
Issuance of common stock to Dominion	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	$ 457,000,000		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	373,000,000		354,000,000
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Derivative Asset	3,000,000		3,000,000
Derivative Liabilities	5,000,000		22,000,000
Virginia Electric and Power Company | Principal Owner | Short-Term Borrowing Arrangements
Related Party Transaction [Line Items]
Payable to affiliates	$ 177,000,000		$ 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.