Significant Accounting Policies (Reconciliation of Total Cash, Restricted Cash and Equivalents) (Detail) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020		Mar. 31, 2020	Dec. 31, 2019
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	[1]	$ 491	$ 179		$ 1,192	$ 166
Restricted cash and equivalents	[2],[3]	71	68		75	103
Cash, restricted cash and equivalents shown in the Consolidated Statements of Cash Flows		562	247		1,267	269
Cash and cash equivalents		477	172	[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		56	35		76	24
Cash and cash equivalents		56	35	[5]	71	17
Restricted cash and equivalents	[3]	$ 0	$ 0		$ 5	$ 7

[1] At March 31, 2021, March 31, 2020, December 31, 2020 and December 31, 2019, Dominion Energy had $14 million, $59 million, $7 million and $31 million of cash and cash equivalents included in current assets held for sale, respectively.

[2] At March 31, 2021, March 31, 2020, December 31, 2020 and December 31, 2019, Dominion Energy had $3 million, $12 million, $3 million and $12 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, 2020 has been derived from the audited Consolidated Balance Sheet at that date.

[5] Virginia Power’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.