Significant Accounting Policies (Reconciliation of Total Cash, Restricted Cash and Equivalents) (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019		Sep. 30, 2019	Dec. 31, 2018
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	[1]	$ 462	$ 166		$ 378	$ 268
Restricted cash and equivalents	[2],[3]	96	103		62	123
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		558	269		440	391
Cash and cash equivalents		413	135	[4]
Virginia Electric and Power Company
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		63	24		37	38
Cash and cash equivalents		62	17	[5]	29	29
Restricted cash and equivalents	[3]	$ 1	$ 7		$ 8	$ 9

[1] At September 30, 2020, September 30, 2019, December 31, 2019 and December 31, 2018, Dominion Energy had $49 million, $80 million, $31 million and $110  million of cash and cash equivalents included in current assets held for sale, respectively.

[2] At September 30, 2020, September 30, 2019, December 31, 2019 and December 31, 2018, Dominion Energy had $16 million, $5 million, $12 million and $89  million of restricted cash and equivalents included in current assets held for sale, respectively

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

[4] Dominion Energy’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.

[5] Virginia Power’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.