Leases (Narrative) (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Leases Disclosure [Line Items]
Property, Plant and Equipment, Net	$ 57,848	$ 57,200	$ 57,848	$ 57,200
Accumulated depreciation, depletion and amortization	25,111	24,843	$ 25,111	24,843
Agreement with Lessor to Complete Construction and Lease Jones Act Compliant Offshore Wind Installation Vessel
Leases Disclosure [Line Items]
Requested cash draws from lessor to fund project costs	$ 187
Required percentage payment for specific full recourse events	100.00%
Lease maturity term	2027-11
New Corporate Office | Agreement with Lessor to Construct and Lease Corporate Office Property
Leases Disclosure [Line Items]
Requested cash draws from lessor to fund project costs		$ 61
Required percentage payment for specific full recourse events		100.00%
Finance lease, option to extend description			At the end of the initial lease term, Dominion Energy can (i) extend the term of the lease for an additional five years, subject to the approval of the participants, at current market terms
Finance lease, option to extend			true
Extension term of lease	5 years		5 years
Required percentage payment to lessor for difference between project costs and sales proceeds			83.00%
Lessor | Agreement with Lessor to Complete Construction and Lease Jones Act Compliant Offshore Wind Installation Vessel
Leases Disclosure [Line Items]
Amount of financing commitments to fund estimated project costs	$ 550		$ 550
Lessor | New Corporate Office | Agreement with Lessor to Construct and Lease Corporate Office Property
Leases Disclosure [Line Items]
Amount of financing commitments to fund estimated project costs		$ 465		465
Power Purchase Arrangement [Member]
Leases Disclosure [Line Items]
Property, Plant and Equipment, Net	2,200	2,800	2,200	2,800
Accumulated depreciation, depletion and amortization	$ 68	$ 364	68	364
Rental revenue			175	174
Depreciation expense			$ 102	$ 94