Regulatory Matters Schedule of Pending Rate Cases (Details) (Details) - Electric Distribution [Member] - USD ($) $ in Millions				12 Months Ended
		Apr. 08, 2019	Jan. 15, 2019	Dec. 31, 2018
Potomac Electric Power Company [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 27
Public Utilities, Requested Return on Equity, Percentage			10.30%
Commonwealth Edison Co [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 57
Public Utilities, Approved Rate Increase (Decrease), Amount				$ (63)
Public Utilities, Requested Equity Capital Structure, Percentage				6.53%
Subsequent Event [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Pending Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	[1]	$ (6)
Public Utilities, Requested Return on Equity, Percentage	[1]	8.90%

[1] Reflects an increase of $57 million for the initial revenue requirement for 2019 and a decrease of $63 million related to the annual reconciliation for 2018. The revenue requirement for 2019 and annual reconciliation for 2018 provides for a weighted average debt and equity return on distribution rate base of 6.53%. See Note 4 — Regulatory Matters of the Exelon 2018 Form 10-K for additional information on ComEd's distribution formula rate filings.