Significant Accounting Policies (Reconciliation of Total Cash, Restricted Cash and Equivalents) (Detail) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash, Cash Equivalents and Restricted Cash [Line Items]
Cash and cash equivalents		$ 268	$ 120	$ 261	$ 607
Restricted cash and equivalents	[1]	123	65	61	25
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		391	185	322	632
Virginia Electric and Power Company
Cash, Cash Equivalents and Restricted Cash [Line Items]
Cash and cash equivalents		29	14	11	18
Restricted cash and equivalents	[1]	9	10
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		38	24	11	18
Dominion Energy Gas Holdings, LLC
Cash, Cash Equivalents and Restricted Cash [Line Items]
Cash and cash equivalents		10	4	23	13
Restricted cash and equivalents	[1]	24	26	20	14
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		$ 34	$ 30	$ 43	$ 27

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