Related-Party Transactions (Narrative) (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Derivative Asset		$ 252,000,000		$ 252,000,000		$ 93,000,000
Derivative Liabilities		776,000,000		776,000,000		740,000,000
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Derivative Asset		145,000,000		145,000,000		24,000,000
Derivative Liabilities		491,000,000		491,000,000		466,000,000
Payable to affiliates		230,000,000		230,000,000		107,000,000	[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]
Payment made to Dominion	$ 313,000,000
Amounts due to Dominion, noncurrent		$ 556,000,000		$ 556,000,000		782,000,000
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		334,000,000		334,000,000		287,000,000
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Derivative Asset		11,000,000		11,000,000		3,000,000
Derivative Liabilities		7,000,000		7,000,000		53,000,000
Virginia Electric and Power Company | Principal Owner | Short-Term Borrowing Arrangements
Related Party Transaction [Line Items]
Payable to affiliates		$ 230,000,000		$ 230,000,000		$ 107,000,000

[1] Virginia Power’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.