Operating Revenue (Schedule of Aggregate Amount of Transaction Price Allocated To Fixed-price Performance Obligations That Unsatisfied At End of Reporting Period And Expected To be Recognized) (Detail1) $ in Millions	Sep. 30, 2020 USD ($)
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 787
Virginia Electric and Power Company
Revenues From Contract With Customer [Line Items]
Revenue, expected to be recognized on multi-year contracts	$ 2