Variable Interest Entities - (Narrative) (Detail) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	May 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) Generator MW
Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Long-term debt			$ 13,453	$ 13,207
Payables to affiliates			121	266
Variable Interest Entity, Primary Beneficiary | SBL Holdco
Variable Interest Entity [Line Items]
Securities due within one year			32
Long-term debt			$ 239
Variable Interest Entity, Primary Beneficiary | Partnership Interest | Merchant Solar Projects
Variable Interest Entity [Line Items]
Initial membership interest percentage			67.00%
Variable Interest Entity Not Primary Beneficiary | Distribution | Atlantic Coast Pipeline | Pipelines | Jointly Owned Natural Gas Pipeline
Variable Interest Entity [Line Items]
Initial membership interest percentage			53.00%
Variable Interest Entity Not Primary Beneficiary | Virginia Electric and Power Company | DES
Variable Interest Entity [Line Items]
Shared Services Purchased			$ 380	349	$ 387
Payables to affiliates			$ 20	$ 175
Variable Interest Entity Not Primary Beneficiary | Partnership Interest | Cove Point
Variable Interest Entity [Line Items]
Initial membership interest percentage			50.00%
Variable Interest Entity V I E And Potential V I E Information Unavailability | Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Long term capacity contract non utility generators (generators) | Generator					1
Aggregate generation capacity from long-term power and capacity contracts (MW) | MW					218
Payment for contract termination	$ 135	$ 135
Payment for contract termination after tax		$ 100
Payment for electric capacity					$ 13
Payment for electric energy					$ 1