Variable Interest Entities - (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Virginia Electric and Power Company
Variable Interest Entity [Line Items]
Long-term debt	$ 12,760		$ 12,760		$ 13,207	[1]
Payables to affiliates	250		250		266	[1]
Variable Interest Entity, Primary Beneficiary | SBL Holdco
Variable Interest Entity [Line Items]
Securities due within one year	35		35		32
Long-term debt	228		228		239
Variable Interest Entity, Not Primary Beneficiary | Virginia Electric and Power Company | DES
Variable Interest Entity [Line Items]
Shared Services Purchased	93	$ 86	189	$ 179
Payables to affiliates	$ 129		$ 129		$ 175

[1] Virginia Power’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.