Operating Revenue (Schedule of Operating Revenue Recognition from Contracts with Customers) (Parenthetical) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Public Utilities General Disclosures [Line Items]
Alternative revenue	$ 15
NGL Midstream
Public Utilities General Disclosures [Line Items]
Sales revenue	241
Renewable Energy Investment Tax Credits
Public Utilities General Disclosures [Line Items]
Sales revenue	17
Virginia Electric and Power Company \| Renewable Energy Investment Tax Credits
Public Utilities General Disclosures [Line Items]
Sales revenue	11
Dominion Energy Gas Holdings, LLC \| NGL Midstream
Public Utilities General Disclosures [Line Items]
Sales revenue	$ 10

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration