Operating Revenue (Narrative) (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Revenues From Contract With Customer [Line Items]
Contract asset balances	$ 44	$ 46
Contract liability balances	102	132
Revenue recognized from contract liability balances	93
Dominion Energy Gas Holdings, LLC
Revenues From Contract With Customer [Line Items]
Contract asset balances	61	66
Contract liability balances	38	41
Revenue recognized from contract liability balances	40
Virginia Electric and Power Company
Revenues From Contract With Customer [Line Items]
Contract liability balances	20	$ 50
Revenue recognized from contract liability balances	$ 25

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130531-203044

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130533-203044

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant