Acquisitions and Dispositions (Dominion Energy Gas Restructuring) (Narrative) (Detail)	Dec. 31, 2019
Cove Point
Business Acquisition And Dispositions [Line Items]
Percentage Of Controlling Ownership	25.00%
Percentage ownership in total units	75.00%
White River Hub
Business Acquisition And Dispositions [Line Items]
Percentage ownership in total units	50.00%
Iroquois
Business Acquisition And Dispositions [Line Items]
Percentage Of Controlling Ownership	25.93%