Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions		Sep. 30, 2022	Dec. 31, 2021
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	$ 2,371	$ 868
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		714	69
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		686	432
Net Amounts		971	367
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	915	464
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		176	35
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		389	90
Net Amounts		350	339
Commodity Contract | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	660	95
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		17	13
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		121	54
Net Amounts		522	28
Commodity Contract | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	233	84
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		13	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		121	54
Net Amounts		99	22
Commodity Contract | Exchange
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	849	374
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		287	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		562	367
Net Amounts		0	0
Commodity Contract | Exchange | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	268	43
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		268	36
Net Amounts		0	0
Interest Rate Contract | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	475	399
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		257	49
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		3	11
Net Amounts		215	339
Interest Rate Contract | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	27	337
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		10	20
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		17	317
Foreign currency exchange rate | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	387	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		153	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		234	0
Foreign currency exchange rate | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	387	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		153	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		$ 234	$ 0

[1] There were no derivative liabilities that are not subject to master netting or similar arrangements at September 30, 2022 or December 31, 2021.

[2] Excludes $2 million and $6 million of derivative liabilities at September 30, 2022 and December 31, 2021, respectively, which are not subject to master netting or similar arrangements.