Subsequent Events - Narrative (Details) - Sale of transmission tower attachment agreements [Member] - Subsequent Event [Member] $ in Millions	Jul. 01, 2020 USD ($)
Pepco Holdings LLC [Member]
Subsequent Event [Line Items]
Marketing Agreement Interest	30.00%
Potomac Electric Power Company [Member]
Subsequent Event [Line Items]
Undivided Interest Sold	60.00%
Agreement Cash Proceeds	$ 98
Agreement Liabilities Recorded	$ 98
Delmarva Power and Light Company [Member]
Subsequent Event [Line Items]
Undivided Interest Sold	60.00%
Agreement Cash Proceeds	$ 13
Agreement Liabilities Recorded	$ 13
Atlantic City Electric Company [Member]
Subsequent Event [Line Items]
Undivided Interest Sold	60.00%
Agreement Cash Proceeds	$ 13
Agreement Liabilities Recorded	$ 13