Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions		Jun. 30, 2020	Dec. 31, 2019
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	$ 1,334	$ 735
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		43	53
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		22	35
Net Amounts		1,269	647
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	985	422
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		5	18
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		980	404
Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet		204	86
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		204	78
Commodity | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	30	105
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		9	21
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		21	84
Commodity | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	5	59
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		5	18
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		0	41
Commodity | Exchange
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	20	21
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		20	21
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		0	0
Interest rate | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	1,272	606
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		14	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		22	35
Net Amounts		1,236	563
Interest rate | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	980	363
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		980	363
Interest rate | Over-the-counter | Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet		192	83
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	5
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		192	78
Foreign currency | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	12	3
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	3
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		12	0
Foreign currency | Over-the-counter | Dominion Energy Gas Holdings, LLC
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet		12	3
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	3
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		$ 12	$ 0

[1] Excludes $— million and $5 million of derivative liabilities at June 30, 2020 and December 31, 2019, respectively, which are not subject to master netting or similar arrangements.

[2] Excludes $19 million and $44 million of derivative liabilities at June 30, 2020 and December 31, 2019, respectively, which are not subject to master netting or similar arrangements.