Variable Interest Entities - (Narrative) (Detail) - Virginia Electric and Power Company - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Variable Interest Entity [Line Items]
Payables to affiliates	$ 168		$ 168		$ 121	[1]
Variable Interest Entity, Not Primary Beneficiary | DES
Variable Interest Entity [Line Items]
Shared Services Purchased	96	$ 89	290	$ 278
Payables to affiliates	$ 27		$ 27		$ 20

[1] Virginia Power’s Consolidated Balance Sheet at December 31, 2021 has been derived from the audited Consolidated Balance Sheet at that date.