Derivatives and Hedge Accounting Activities (Schedule of Offsetting Assets) (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		$ 493	$ 396	[1]
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		69	46
Net Amounts		424	350
Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	271	178
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		35	14
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received			0
Net Amounts		236	164
Commodity | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		153	117	[1]
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		13	9
Net Amounts		140	108
Commodity | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	110	111
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		8	6
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received			0
Net Amounts		102	105
Commodity | Exchange
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		9	49	[1]
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		7	24
Net Amounts		2	25
Commodity | Exchange | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	7	1
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		7	1
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received			0
Net Amounts			0
Interest rate | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		323	230	[1]
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		49	13
Net Amounts		274	217
Interest rate | Over-the-counter | Virginia Electric and Power Company
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet	[2]	146	66
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments		20	7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received			0
Net Amounts		126	59
Foreign currency exchange rate | Over-the-counter
Offsetting Assets [Line Items]
Gross Assets Presented in the Consolidated Balance Sheet		8
Net Amounts		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]	8
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments			0
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received			0
Net Amounts		$ 8	$ 0

[1] Excludes $120 million and $1 million of derivative assets at December 31, 2021 and 2020, respectively, which are not subject to master netting or similar arrangements.

[2] Excludes $29 million and $3 million of derivative assets at December 31, 2021 and 2020, respectively, which are not subject to master netting or similar arrangements.