Regulatory Matters - Additional Information (Detail)								1 Months Ended														6 Months Ended	24 Months Ended
	May. 19, 2015 USD ($)	Apr. 17, 2015 USD ($)	Dec. 08, 2014	Dec. 07, 2014	Apr. 15, 2014 USD ($)	Sep. 20, 2013 USD ($)	Feb. 28, 2013	Mar. 31, 2015 USD ($)	Oct. 31, 2014	Aug. 31, 2014 USD ($)	Jul. 31, 2014 USD ($)	May. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Oct. 31, 2013 USD ($)	Jul. 31, 2013 USD ($)	Mar. 31, 2013 USD ($)	Feb. 28, 2013	Nov. 30, 2012 USD ($)	Jul. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Apr. 30, 2012 MW
Public Utilities, General Disclosures [Line Items]
Requested rate change						$ 39,000,000														$ 18,100,000
Return on equity, percentage																				9.31%	10.75%
Effect of proposed change on Gas Cost Rate										7.40%
Adjusted rate change					$ 37,400,000
Consolidated tax adjustment calculation review period									5 years
Percentage of revenue requirement related to consolidated tax adjustment calculation									25.00%
New power plant output | MW																								661
Undergrounding project cost												$ 1,000,000,000
Bear estimated complete project												500,000,000
Merger agreement																						Following informal discussions with the DOJ, effective as of September 5, 2014, Exelon withdrew its Notification and Report Form and refiled it on September 9, 2014, which restarted the waiting period required by the HSR Act. On October 9, 2014, each of Pepco Holdings and Exelon received a request for additional information and documentary material from the DOJ, which had the effect of extending the DOJ review period until 30 days after each of Pepco Holdings and Exelon certified that it has substantially complied with the request.
Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage			8.80%	10.80%
ROE determined, description																						Each ten basis point reduction in the ROE would result in an increase in required reserves and a reduction of PHI’s operating income of $2.4 million.
Reduction in operating income																						$ 2,400,000
Expected [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change											$ 8,750,000			$ 43,300,000							$ 68,400,000
Return on equity, percentage											9.62%			10.25%
Actual [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																					66,200,000
District of Columbia [Member] | DC Undergrounding Task Force [Member]
Public Utilities, General Disclosures [Line Items]
Underground project cost												375,000,000
Minimum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output | MW																								650
Maximum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output | MW																								700
Maximum [Member] | District of Columbia [Member] | Department of Transportation [Member]
Public Utilities, General Disclosures [Line Items]
Under grounding project costs covered by existing capital projects program												125,000,000
Delmarva Power & Light Co/De [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change						$ 39,000,000				$ 15,100,000					$ 56,000,000		$ 42,000,000
Return on equity, percentage										9.70%							10.25%					10.80%
Increased distribution base period															4 years
Estimated return on equity, year one															7.41%
Estimated return on equity, year two															8.80%
Estimated return on equity, year three															9.75%
Estimated return on equity, year four															9.75%
Customer refundable fees															$ 500,000
Effect of proposed change on Gas Cost Rate										7.40%
Basis-point																						0.50%	0.50%
New power plant output | MW																								661
Additional interim rate increase implemented										$ 15,100,000
Delmarva Power & Light Co/De [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage			8.80%	10.80%														8.70%				11.30%
ROE determined, description																						Each ten basis point reduction in the ROE would result in an increase in required reserves and a reduction of DPL’s operating income of $0.8 million.
Reduction in operating income																						$ 800,000
Delmarva Power & Light Co/De [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output | MW																								650
Delmarva Power & Light Co/De [Member] | Minimum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																		6.78%
Delmarva Power & Light Co/De [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output | MW																								700
Delmarva Power & Light Co/De [Member] | Maximum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																		10.33%
Potomac Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																				$ 18,100,000	$ 68,400,000
Return on equity, percentage																9.36%			10.25%	9.31%	10.75%	10.80%
Requested rate change																$ 27,900,000
Charges on cost of recovery																$ 24,000,000
Adjusted rate change					$ 37,400,000
Basis-point																						0.50%	0.50%
New power plant output | MW																								661
Undergrounding project cost												1,000,000,000
Bear estimated complete project												500,000,000
Return on equity, percentage																9.36%
Potomac Electric Power Co [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage			8.80%	10.80%			8.70%											8.70%				11.30%
ROE determined, description																						Each ten basis point reduction in the ROE would result in an increase in required reserves and a reduction of Pepco’s operating income of $1 million.
Reduction in operating income																						$ 1,000,000
Potomac Electric Power Co [Member] | Expected [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change											$ 8,750,000			$ 43,300,000					$ 60,800,000
Return on equity, percentage											9.62%			10.25%
Potomac Electric Power Co [Member] | Actual [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																					$ 66,200,000
Potomac Electric Power Co [Member] | District of Columbia [Member] | DC Undergrounding Task Force [Member]
Public Utilities, General Disclosures [Line Items]
Underground project cost												375,000,000
Potomac Electric Power Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output | MW																								650
Potomac Electric Power Co [Member] | Minimum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							6.78%											6.78%
Potomac Electric Power Co [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output | MW																								700
Potomac Electric Power Co [Member] | Maximum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							10.33%											10.33%
Potomac Electric Power Co [Member] | Maximum [Member] | District of Columbia [Member] | Department of Transportation [Member]
Public Utilities, General Disclosures [Line Items]
Under grounding project costs covered by existing capital projects program												$ 125,000,000
Atlantic City Electric Co [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage																						10.80%
Overall annual rate increase as net impact of proposed changes	$ 33,900,000	$ 33,900,000						$ 52,000,000					$ 52,000,000
Contributions received by ACE																						$ 11,000,000	$ 11,000,000
Consolidated tax adjustment calculation review period									5 years
Percentage of revenue requirement related to consolidated tax adjustment calculation									25.00%
Basis-point																						0.50%	0.50%
Atlantic City Electric Co [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage			8.80%	10.80%			8.70%															11.30%
ROE determined, description																						Each ten basis point reduction in the ROE would result in an increase in required reserves and a reduction of ACE’s operating income of $0.6 million.
Reduction in operating income																						$ 600,000
Atlantic City Electric Co [Member] | Minimum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							6.78%
Atlantic City Electric Co [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Contributions paid by ACE																							$ 1,000,000
Atlantic City Electric Co [Member] | Maximum [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage							10.33%