Regulatory Matters Annual Electric Transmission Fillings (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 44
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 11
Public Utilities, Approved Return on Equity, Percentage	11.50%
Public Utilities, Approved Equity Capital Structure, Percentage	8.43%
Prior Year Revenue Adjustment	$ (33)
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	31
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 26
Public Utilities, Approved Return on Equity, Percentage	10.50%
Public Utilities, Approved Equity Capital Structure, Percentage	7.47%
Prior Year Revenue Adjustment	$ 3
Proposed Capital Expenditure	$ (8)
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	10.50%
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Proposed Capital Expenditure	$ (29)