Fair Value of Financial Assets and Liabilities - Fair Value Assets and Liabilities Measure on a Recurring Basis Gain Loss Included in Earnings (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	$ 804	$ 409
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	(1,214)	11
Operating Revenue [Member]
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	(1,343)	(404)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	(1,577)	(31)
Purchased Power And Fuel [Member]
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	531	(10)
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	355	37
Operating and Maintenance [Member]
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	3	3
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	3
Other, net [Member]
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	5	2
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	5	2
Pepco Holdings LLC [Member] | Operating and Maintenance [Member]
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	3	3
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	3	3
Potomac Electric Power Company [Member] | Operating and Maintenance [Member]
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	3	3
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 3	$ 3