Regulatory Matters - Additional Information (Detail) (USD $)	0 Months Ended		1 Months Ended					3 Months Ended	1 Months Ended								0 Months Ended		1 Months Ended
	Apr. 15, 2014	Sep. 20, 2013	Oct. 31, 2014	Aug. 31, 2014	May 31, 2014	Jul. 31, 2012	Dec. 31, 2011	Mar. 31, 2015	Dec. 31, 2014	Jul. 31, 2014	Dec. 31, 2013	Oct. 31, 2013	Mar. 31, 2013	Feb. 28, 2013	Jul. 31, 2013	Nov. 30, 2012	Feb. 28, 2013	Apr. 16, 2014	Mar. 31, 2015	Mar. 31, 2014	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																					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%
One-time reduction on settlement				225,000
One-time payment on settlement				258,500
ROE determined, description								Each ten basis point reduction in the ROE would result in a reduction of PHI's operating income of $1.9 million.
Reduction in operating income								1,900,000
Expected [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change							68,400,000			8,750,000	43,300,000
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																					650
Maximum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output																					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%				10.80%					10.25%
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								50.00%											50.00%
New power plant output																					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								11.30%	8.80%					8.70%
One-time reduction on settlement								225,000
One-time payment on settlement								258,500
ROE determined, description								Each ten basis point reduction in the ROE would result in a reduction of DPL's operating income of $0.6 million.
Reduction in operating income								600,000
Delmarva Power & Light Co/De [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
New power plant output																					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																					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						9.31%	10.75%	10.80%							9.36%	10.25%
Requested rate change															27,900,000
Charges on cost of recovery															24,000,000
Adjusted rate change	37,400,000
Basis-point								50.00%											50.00%
New power plant output																					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								11.30%	8.80%					8.70%			8.70%
ROE determined, description								Each ten basis point reduction in the ROE would result in a reduction of Pepco's operating income of $0.8 million.
Reduction in operating income								800,000
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																					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																					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 decrease as net impact of adjusting charges					41,100,000													41,100,000	52,000,000	24,500,000
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								50.00%											50.00%
Atlantic City Electric Co [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Return on equity, percentage								11.30%	8.80%								8.70%
ROE determined, description								Each ten basis point reduction in the ROE would result in a reduction of ACE's operating income of $0.5 million.
Reduction in operating income								500,000
Atlantic City Electric Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Contributions received by ACE								1,000,000											1,000,000
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 received by ACE								1,000,000											$ 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%