Derivatives and Hedge Accounting Activities (Schedule of Offsetting Assets) (Detail) - USD ($) $ in Millions		Sep. 30, 2022	Dec. 31, 2021
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	$ 2,258	$ 493
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		714	69
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		1,544	424
Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	899	271
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		176	35
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		723	236
Commodity Contract | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	367	153
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		11	13
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		356	140
Commodity Contract | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	297	110
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		7	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		290	102
Commodity Contract | Exchange
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	292	9
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		287	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		5	2
Commodity Contract | Exchange | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	0	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		0	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		0	0
Interest Rate Contract | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	1,593	323
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		410	49
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		1,183	274
Interest Rate Contract | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	596	146
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		163	20
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		433	126
Foreign currency exchange rate | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[1]	6	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		6	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		0	8
Foreign currency exchange rate | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	6	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		6	0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received		0	0
Net Amounts		$ 0	$ 8

[1] Excludes $211 million and $120 million of derivative assets at September 30, 2022 and December 31, 2021, respectively, which are not subject to master netting or similar arrangements.

[2] Excludes $62 million and $29 million of derivative assets at September 30, 2022 and December 31, 2021, respectively, which are not subject to master netting or similar arrangements.