Derivatives and Hedge Accounting Activities (Schedule of Offsetting Assets) (Detail) - USD ($) $ in Millions		Jun. 30, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	$ 215	$ 91
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		43	53
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		7	0
Net Amounts		165	38
Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	129	21
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		5	18
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		124	3
Dominion Energy Gas Holdings, LLC
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		0	0
Commodity | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	136	35
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		9	21
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		127	14
Commodity | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	129	19
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		5	18
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		124	1
Commodity | Exchange
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	45	37
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		20	21
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		7	0
Net Amounts		18	16
Interest rate | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	34	11
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		14	3
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		20	8
Foreign currency | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		0	0
Foreign currency | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	0	2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		0	2
Foreign currency | Over-the-counter | Dominion Energy Gas Holdings, LLC
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		$ 0	$ 0

[1] Excludes $1 million and $2 million of derivative assets at June 30, 2020 and December 31, 2019, respectively, which are not subject to master netting or similar arrangements.

[2] Excludes $4 million and $3 million of derivative assets at June 30, 2020 and December 31, 2019, respectively, which are not subject to master netting or similar arrangements.