Significant Financing Transactions (Narrative) (Detail)		1 Months Ended					2 Months Ended	3 Months Ended
		Apr. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) facility	Feb. 28, 2018 USD ($) agreement	Jan. 31, 2018 USD ($) shares	Jun. 30, 2017 USD ($) agreement	Apr. 30, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($) facility shares	Mar. 31, 2017 USD ($) shares	May 03, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Number of joint revolving credit facilities | facility			2					2
Short-term debt			$ 2,713,000,000					$ 2,713,000,000			$ 3,298,000,000	[1]
Issuance of common stock								580,000,000	$ 79,000,000
Aggregate proceeds from issuance of shares of common stock								$ 581,000,000	$ 79,000,000
Common Stock
Debt Instrument [Line Items]
Issuance of common stock (in shares) | shares								8,000,000	1,000,000
Issuance of common stock								$ 580,000,000	$ 79,000,000
Shelf Registration For Sale Of Common Stock Through At Market Program
Debt Instrument [Line Items]
Number of sales agency agreements | agreement				6		3
Issuance of common stock (in shares) | shares					6,600,000
Issuance of common stock				$ 0	$ 495,000,000
Fees and commissions paid					5,000,000
Shelf Registration For Sale Of Common Stock Through At Market Program | Maximum
Debt Instrument [Line Items]
Sale of stock authorized amount				1,000,000,000		$ 500,000,000
Subsequent Event | Common Stock | Forward Sale Agreements
Debt Instrument [Line Items]
Issuance of shares of common stock under forward equity sale agreement | shares							20,000,000
Aggregate proceeds from issuance of shares of common stock							$ 1,500,000,000
Subsequent Event | Maximum | Common Stock | Forward Sale Agreements
Debt Instrument [Line Items]
Full physical settlement of forward sale agreements date							Dec. 31, 2018
Subsequent Event | Underwriters Option to Purchase | Common Stock | Forward Sale Agreements
Debt Instrument [Line Items]
Issuance of shares of common stock under option to purchase | shares							2,100,000
Issuance of shares of common stock under option to purchase, price per share | $ / shares		$ 67.33					$ 67.33
Period to purchase common stock under option							30 days
Subsequent Event | Underwriters Option to Purchase | Maximum | Common Stock | Forward Sale Agreements
Debt Instrument [Line Items]
Issuance of shares of common stock under option to purchase | shares							3,000,000
Dominion Energy Midstream Partners, LP | Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit			500,000,000					500,000,000
Guarantee recorded amount			$ 0					0
Line of credit facility maturity date			Mar. 31, 2021
Dominion Energy Midstream Partners, LP | Revolving Credit Facility | Letter of Credit
Debt Instrument [Line Items]
Facility Limit			$ 250,000,000					250,000,000
Dominion Energy Midstream Partners, LP | Revolving Credit Facility | Subsequent Event
Debt Instrument [Line Items]
Guarantee recorded amount										$ 73,000,000
Virginia Electric and Power Company
Debt Instrument [Line Items]
Short-term debt			426,000,000					426,000,000			$ 542,000,000	[2]
Credit facility			100,000,000					$ 100,000,000
Issuance of common stock (in shares) | shares								0	0
Virginia Electric and Power Company | Tax Exempt Financing
Debt Instrument [Line Items]
Repayment of variable rate tax-exempt financings			100,000,000
$6 billion Joint Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit	[3]		6,000,000,000					$ 6,000,000,000
$6 billion Joint Revolving Credit Facility | Questar Gas
Debt Instrument [Line Items]
Facility Limit			250,000,000					250,000,000
$6 billion Joint Revolving Credit Facility | Virginia Electric and Power Company
Debt Instrument [Line Items]
Facility Limit	[4]		6,000,000,000					6,000,000,000
Credit Facilities, Maturing in December 2017 with 1 year Automatic Renewals through 2023 | SBL Holdco
Debt Instrument [Line Items]
Facility Limit			30,000,000					$ 30,000,000
Automatic renewal period								1 year
Short-term debt			0					$ 0
Credit Facilities, Maturing in May 2018 with 1 year Automatic Renewals through 2024 | Dominion Solar Projects III, Inc
Debt Instrument [Line Items]
Facility Limit			25,000,000					$ 25,000,000
Automatic renewal period								1 year
Short-term debt			0					$ 0
Term Loan Credit Agreement
Debt Instrument [Line Items]
Guarantee recorded amount				$ 950,000,000
Duration of credit facilities				364 days
Maximum allowed total debt to total capital ratio				67.50%
3.53% Due 2028 | Dominion Energy Midstream Partners, LP | Private Placement
Debt Instrument [Line Items]
Total Long-term Debt					$ 100,000,000
Interest rate percentage					3.53%
Debt maturity year					2028
3.91% Due 2038 | Dominion Energy Midstream Partners, LP | Private Placement
Debt Instrument [Line Items]
Total Long-term Debt					$ 150,000,000
Interest rate percentage					3.91%
Debt maturity year					2038
Senior Notes, Due in 2028 | Virginia Electric and Power Company | Senior Notes
Debt Instrument [Line Items]
Total Long-term Debt			$ 700,000,000					$ 700,000,000
Interest rate percentage			3.80%					3.80%
Debt maturity year			2028
3.30% Due 2030 | Questar Gas | Subsequent Event | Private Placement
Debt Instrument [Line Items]
Total Long-term Debt		$ 50,000,000					$ 50,000,000
Interest rate percentage		3.30%					3.30%
Debt maturity year		2030
3.97% Due 2047 | Questar Gas | Subsequent Event | Private Placement
Debt Instrument [Line Items]
Total Long-term Debt		$ 100,000,000					$ 100,000,000
Interest rate percentage		3.97%					3.97%
Debt maturity year		2047

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

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

[3] This credit facility matures in March 2023 and can be used by the Companies to support bank borrowings and the issuance of commercial paper, as well as to support up to a combined $2.0 billion of letters of credit.

[4] The full amount of the facility is available to Virginia Power, less any amounts outstanding to co-borrowers Dominion Energy, Dominion Energy Gas and Questar Gas. The sub-limit for Virginia Power is set within the facility limit but can be changed at the option of the Companies multiple times per year. At March 31, 2018, the sub-limit for Virginia Power was $1.5 billion. If Virginia Power has liquidity needs in excess of its sub-limit, the sub-limit may be changed or such needs may be satisfied through short-term intercompany borrowings from Dominion Energy. This credit facility matures in March 2023 and can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $2.0 billion (or the sub-limit, whichever is less) of letters of credit.