Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions		Jun. 30, 2022	Dec. 31, 2021
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	$ 1,650	$ 868
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		464	69
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		690	432
Net Amounts		496	367
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	576	464
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		61	35
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		287	90
Net Amounts		228	339
Commodity Contract | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	463	95
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		21	13
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		116	54
Net Amounts		326	28
Commodity Contract | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	222	84
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		5	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		116	54
Net Amounts		101	22
Commodity Contract | Exchange
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	741	374
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		170	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		571	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]	173	43
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		2	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		171	36
Net Amounts		0	0
Interest Rate Contract | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	333	399
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		252	49
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		3	11
Net Amounts		78	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]	68	337
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		33	20
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		35	317
Foreign currency exchange rate | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	113	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		21	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		92	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]	113	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		21	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		$ 92	$ 0

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

[2] Excludes $9 million and $6 million of derivative liabilities at June 30, 2022 and December 31, 2021, respectively, which are not subject to master netting or similar arrangements.