Goodwill and Intangible Assets (Components of Intangible Assets) (Detail) - Computer Software, Intangible Asset [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,043	$ 955
Accumulated Amortization	358	337
Virginia Electric and Power Company
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	347	326
Accumulated Amortization	114	101
Dominion Energy Gas Holdings, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	165	147
Accumulated Amortization	$ 56	$ 49

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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