Income Taxes - Settlement of Income Tax Audits, Refund Claims, and Litigation (Details) $ in Millions	Sep. 30, 2020 USD ($)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 14
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	14
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 14