Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Parenthetical) (Detail) - Foreign currency	Sep. 30, 2018 EUR (€)
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros)	€ 250,000,000
Dominion Energy Gas Holdings, LLC
Derivative [Line Items]
Interest rate / Foreign currency (US Dollars, Euros)	€ 250,000,000

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant