Regulatory Matters Annual Electric Transmission Fillings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			$ 90
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 94
Public Utilities, Approved Return on Equity, Percentage			11.50%
Public Utilities, Approved Equity Capital Structure, Percentage			8.47%	8.61%
Prior Year Revenue Adjustment			$ 4
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			12
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ 28
Public Utilities, Approved Return on Equity, Percentage			10.50%
Public Utilities, Approved Equity Capital Structure, Percentage			8.09%	8.46%
Prior Year Revenue Adjustment			$ 3
Proposed Capital Expenditure			13
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			2
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ (23)
Public Utilities, Approved Return on Equity, Percentage		10.60%
Public Utilities, Approved Return on Equity, Percentage			10.50%
Public Utilities, Approved Equity Capital Structure, Percentage			7.88%	8.36%
Prior Year Revenue Adjustment	$ (10)
Current Year Revenue Adjustment			$ (15)
Delmarva Power and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			8
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ (14)
Public Utilities, Approved Return on Equity, Percentage			10.50%
Public Utilities, Requested Equity Capital Structure, Percentage	10.60%
Public Utilities, Approved Equity Capital Structure, Percentage			7.21%	7.80%
Prior Year Revenue Adjustment	$ (10)
Current Year Revenue Adjustment			$ (12)
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount			8
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			$ (6)
Public Utilities, Approved Return on Equity, Percentage			10.50%
Public Utilities, Approved Equity Capital Structure, Percentage			7.83%	8.51%
Prior Year Revenue Adjustment	$ (14)
Current Year Revenue Adjustment			$ 0