Significant Financing Transactions (Narrative) (Detail)			1 Months Ended								2 Months Ended	3 Months Ended				6 Months Ended	9 Months Ended
		Nov. 07, 2018 USD ($)	Oct. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	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	Sep. 30, 2018 USD ($) shares		Mar. 31, 2018 USD ($) facility	Sep. 30, 2017 shares	Jun. 30, 2018 USD ($) shares	Sep. 30, 2018 USD ($) shares		Sep. 30, 2017 USD ($) shares	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Number of joint revolving credit facilities | facility							2							2
Short-term debt												$ 2,935,000,000					$ 2,935,000,000			$ 3,298,000,000	[1]
Guarantee recorded amount												73,000,000					73,000,000
Issuance of common stock																	737,000,000		$ 1,232,000,000
Aggregate proceeds from issuance of shares of common stock																	$ 737,000,000		$ 1,233,000,000
Common Stock
Debt Instrument [Line Items]
Issuance of common stock (in shares) | shares																	10,000,000		16,000,000
Issuance of common stock																	$ 737,000,000		$ 1,232,000,000
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
Maximum | Common Stock | Forward Sale Agreements
Debt Instrument [Line Items]
Full physical settlement of forward sale agreements date											Dec. 31, 2018
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
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
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 | Limited Partner | Dominion Midstream Limited Partner Common Unit Purchase Program
Debt Instrument [Line Items]
Common units conversion basis																	In May 2018, all of the subordinated units of Dominion Energy Midstream held by Dominion Energy were converted into common units on a 1:1 ratio following the payment of Dominion Energy Midstream’s distribution for the first quarter of 2018.
Common units conversion basis ratio														100.00%
Number of common units received on incentive distribution right | shares																27,000,000
Change in noncontrolling interest																$ 375,000,000
Dominion Energy Midstream Partners, LP | Letter of Credit
Debt Instrument [Line Items]
Facility Limit							$ 250,000,000							$ 250,000,000
Dominion Energy Midstream Partners, LP | Letter of Credit | Subsequent Event
Debt Instrument [Line Items]
Facility Limit			$ 21,000,000
Facility limit, current borrowing			$ 16,000,000
Line of credit facility, termination date			Jun. 30, 2020
Dominion Energy Midstream Partners, LP | Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit							$ 500,000,000							500,000,000
Line of credit facility maturity date							Mar. 31, 2021
Guarantee recorded amount												73,000,000					$ 73,000,000
Virginia Electric and Power Company
Debt Instrument [Line Items]
Short-term debt												$ 934,000,000					$ 934,000,000			542,000,000	[2]
Credit facility							$ 100,000,000							100,000,000
Issuance of common stock (in shares) | shares												0			0		0		0
Virginia Electric and Power Company | Tax Exempt Financing
Debt Instrument [Line Items]
Repayment of variable rate tax-exempt financings							100,000,000
Dominion Energy Gas Holdings, LLC
Debt Instrument [Line Items]
Short-term debt												$ 141,000,000					$ 141,000,000			$ 629,000,000	[3]
$6 billion Joint Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit							6,000,000,000					6,000,000,000	[4]	6,000,000,000			6,000,000,000	[4]
Facility Capacity Available	[4]											2,940,000,000					2,940,000,000
$6 billion Joint Revolving Credit Facility | Letter of Credit
Debt Instrument [Line Items]
Facility Limit												2,000,000,000					2,000,000,000
$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	[5]											6,000,000,000					6,000,000,000
$6 billion Joint Revolving Credit Facility | Virginia Electric and Power Company | Letter of Credit
Debt Instrument [Line Items]
Facility Limit												2,000,000,000					2,000,000,000
$6 billion Joint Revolving Credit Facility | Dominion Energy Gas Holdings, LLC
Debt Instrument [Line Items]
Facility Limit	[6]											1,500,000,000					1,500,000,000
$6 billion Joint Revolving Credit Facility | Dominion Energy Gas Holdings, LLC | Letter of Credit
Debt Instrument [Line Items]
Facility Limit												1,500,000,000					1,500,000,000
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 [Member]
Debt Instrument [Line Items]
Guarantee recorded amount				$ 500,000,000				$ 950,000,000								500,000,000
Duration of credit facilities				364 days				364 days
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 | Senior Notes
Debt Instrument [Line Items]
Total Long-term Debt				$ 300,000,000												$ 300,000,000
Interest rate percentage				4.25%												4.25%
Debt maturity year				2028
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 | 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 | 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
Senior Notes, Due in 2020 | Senior Notes
Debt Instrument [Line Items]
Total Long-term Debt					$ 500,000,000
Debt maturity year					2020
Senior Notes, Due in 2021 | Dominion Energy Gas Holdings, LLC | Senior Notes
Debt Instrument [Line Items]
Total Long-term Debt				$ 500,000,000												$ 500,000,000
Debt maturity year				2021
Credit Facility Matures in 2021 | Cove Point
Debt Instrument [Line Items]
Facility Limit												3,000,000,000					3,000,000,000
Guarantee recorded amount												2,000,000,000					2,000,000,000
Facility Capacity Available												$ 1,000,000,000					$ 1,000,000,000
Senior Notes Mature in December 2042 | Cove Point | Subsequent Event | Private Placement
Debt Instrument [Line Items]
Total Long-term Debt		$ 362,000,000
Interest rate percentage		4.82%
Debt instrument maturity month and year		2042-12

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

[4] 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.

[5] 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 September 30, 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.

[6] A maximum of $1.5 billion of the facility is available to Dominion Energy Gas, assuming adequate capacity is available after giving effect to uses by co-borrowers Dominion Energy, Virginia Power and Questar Gas. The sub-limit for Dominion Energy Gas is set within the facility limit but can be changed at the option of the Companies multiple times per year. At September 30, 2018, the sub-limit for Dominion Energy Gas was $750 million. If Dominion Energy Gas 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 $1.5 billion (or the sub-limit, whichever is less) of letters of credit.