Significant Accounting Policies (Reconciliation of Total Cash, Restricted Cash and Equivalents (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017		Jun. 30, 2017	Dec. 31, 2016
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents		$ 190	$ 120	[1]	$ 260	$ 261
Restricted cash and equivalents	[2]	164	65		64	61
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		354	185		324	322
Virginia Electric and Power Company
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents		20	14	[3]	44	11
Restricted cash and equivalents	[2]	10	10
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		30	24		44	11
Dominion Energy Gas Holdings, LLC
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents		5	4	[4]	4	23
Restricted cash and equivalents	[2]	24	26		30	20
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		$ 29	$ 30		$ 34	$ 43

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

[2] Restricted cash and equivalent balances are presented within other current assets in the Companies’ Consolidated Balance Sheets.

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

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