Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Detail) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	$ 1,314	$ 868
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		325	69
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		622	432
Net Amounts		367	367
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	507	464
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		55	35
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		251	90
Net Amounts		201	339
Commodity Contract | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	326	95
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		37	13
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		124	54
Net Amounts		165	28
Commodity Contract | Over-the-counter | Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[2]	167	84
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		10	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		124	54
Net Amounts		33	22
Commodity Contract | Exchange
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	622	374
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		130	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		492	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]	136	43
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		9	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		127	36
Net Amounts		0	0
Interest Rate Contract | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	362	399
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		158	49
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		6	11
Net Amounts		198	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]	200	337
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		36	20
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral		0	0
Net Amounts		164	317
Foreign currency exchange rate | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Liabilities Presented in the Consolidated Balance Sheet	[1]	4	0
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		4	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]	4	0
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		$ 4	$ 0

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

[2] Excludes $1 million and $6 million of derivative liabilities at March 31, 2022 and December 31, 2021, respectively, which are not subject to master netting or similar arrangements.