Regulatory Assets and Liabilities (Narrative) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Public Utilities, General Disclosures [Line Items]
Regulatory assets past expenditures not earning return		$ 382
Regulatory assets		$ 2,698	$ 2,480	[1]
Period for which expenditures are expected to be recovered		2 years
PJM transmission rates
Public Utilities, General Disclosures [Line Items]
Regulatory assets	[2]	$ 229	222
Virginia Electric and Power Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets past expenditures not earning return		304
Regulatory assets		1,009	810	[3]
Virginia Electric and Power Company | PJM transmission rates
Public Utilities, General Disclosures [Line Items]
Regulatory assets	[2]	$ 229	$ 222

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

[2] Reflects amounts related to the PJM transmission cost allocation matter. See Note 13 for more information.

[3] Virginia Power’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.