Regulatory Matters Net Regulatory Asset or Liability (Details) (Details) - Federal Energy Regulatory Commission [Member] - Electric Transmission [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	$ 60	$ 43
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	31	31
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	17	12
Pepco Holdings, LLC [Member] | Predecessor [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets		14
Pepco Holdings, LLC [Member] | Successor [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	12
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	4	5
Delmarva Power and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	7	7
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
Net Regulatory Assets	$ 1	$ 2