Related-Party Transactions (Narrative) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Derivative Asset	$ 244,000,000			$ 307,000,000
Derivative Liabilities	90,000,000			284,000,000
Virginia Electric and Power Company
Related Party Transaction [Line Items]
Derivative Asset	129,000,000	[1]		166,000,000
Derivative Liabilities	23,000,000			66,000,000
Short term demand note	11,000,000			33,000,000	[2]
Outstanding borrowings, net of repayments, under money pool for non-regulated subsidiaries	$ 0			0
Issuance of common stock (in shares)	0		0
Virginia Electric and Power Company | Pension Benefits | Amounts Associated with the Dominion Pension Plan
Related Party Transaction [Line Items]
Amounts due to Dominion, noncurrent	$ 537,000,000			505,000,000
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	218,000,000			199,000,000
Virginia Electric and Power Company | Affiliated Entity
Related Party Transaction [Line Items]
Derivative Asset	5,000,000			11,000,000
Derivative Liabilities	7,000,000			5,000,000
Virginia Electric and Power Company | Principal Owner
Related Party Transaction [Line Items]
Short term demand note	11,000,000			33,000,000
Dominion Energy Gas Holdings, LLC
Related Party Transaction [Line Items]
Derivative Asset	44,000,000			32,000,000
Derivative Liabilities	1,000,000			8,000,000
Short term demand note	41,000,000			18,000,000	[3]
Dominion Energy Gas Holdings, LLC | Revolving Credit Facility | IRCA
Related Party Transaction [Line Items]
Short term demand note	41,000,000			18,000,000
Dominion Energy Gas Holdings, LLC | Maximum
Related Party Transaction [Line Items]
Derivative Asset	1,000,000
Derivative Liabilities	1,000,000
Dominion Energy Gas Holdings, LLC | Pension Benefits | Amounts Associated with the Dominion Pension Plan
Related Party Transaction [Line Items]
Amounts due from Dominion, noncurrent	744,000,000			734,000,000
Dominion Energy Gas Holdings, LLC | 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	$ 9,000,000			$ 7,000,000

[1] Noncurrent derivative assets are presented in other deferred charges and other assets in Virginia Power's Consolidated Balance Sheets.

[2] Virginia Power’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

[3] Dominion Energy Gas’ Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.