Regulatory Matters - Additional Information (Detail) (USD $)	0 Months Ended								1 Months Ended			12 Months Ended		0 Months Ended				3 Months Ended	12 Months Ended	0 Months Ended											1 Months Ended	0 Months Ended			1 Months Ended
	Oct. 22, 2014	Aug. 29, 2014	Aug. 20, 2014	May 03, 2014	Apr. 15, 2014	Mar. 31, 2014	Mar. 26, 2014	Sep. 20, 2013	Feb. 28, 2014	Jul. 31, 2012	Dec. 31, 2011	Dec. 31, 2014 mi	Dec. 31, 2013	Jul. 02, 2014	Dec. 04, 2013	Dec. 08, 2014	Aug. 25, 2014	Jun. 30, 2014	Dec. 31, 2011	Dec. 31, 2014	Aug. 19, 2014	Aug. 05, 2014	Oct. 02, 2013	Mar. 22, 2013	Feb. 28, 2013	Dec. 03, 2013	Jul. 12, 2013	Mar. 08, 2013	Nov. 30, 2012	Aug. 24, 2012 mi	Feb. 28, 2013	Apr. 16, 2014	Mar. 14, 2014	Mar. 03, 2014	May 31, 2014	Apr. 30, 2012 MW	Jul. 11, 2014
Public Utilities, General Disclosures [Line Items]
Transition bond maturity, lower range												2015
Transition bond maturity, upper range												2023
Requested rate change			$ 19,000,000			$ 61,700,000	$ 23,400,000	$ 39,000,000		$ 18,100,000
Return on equity, percentage			9.75%			10.25%	9.40%			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
Abandonment costs sought									88,000,000			80,500,000	82,000,000
Recovery period												3 years
Estimated fair value of real property acquired									8,000,000
Length transmission line												152
Abandonment costs												33,000,000								33,000,000
Land held for future use in utility operations												8,000,000								8,000,000
Period to issue decision												180 days
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.
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
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 $1.5 million.
Reduction in operating income																		1,500,000
2015 [Member]
Public Utilities, General Disclosures [Line Items]
Expected pre-tax income related to abandonment costs												1,000,000
District of Columbia [Member] | DC Undergrounding Task Force [Member]
Public Utilities, General Disclosures [Line Items]
Underground project cost				375,000,000
Advanced Metering Infrastructure Costs [Member]
Public Utilities, General Disclosures [Line Items]
Base rates period												15 years
Related portion of advanced metering infrastructure																																					50.00%
Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Storm Restoration Costs Amortization and recovery period																			3 years
Regulatory asset, amortization period, years												1 year
New power plant output																																				650
Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Incremental Storm Restoration Costs Amortization and recovery period																			5 years
Regulatory asset, amortization period, years												20 years
New power plant output																																				700
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												10.80%										9.70%		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
Abandonment costs sought									38,000,000			36,600,000	37,000,000
Recovery period									3 years
Estimated fair value of real property acquired									6,000,000
Length transmission line												152
Land held for future use in utility operations												6,000,000								6,000,000
Period to issue decision																					180 days
Regulatory asset related to MAPP abandonment costs																				14,000,000
Goodwill transferred to a regulatory asset												41,000,000								41,000,000
Return earned on regulatory assets												12.95%								12.95%
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 $0.5 million.
Reduction in operating income																		500,000
Delmarva Power & Light Co/De [Member] | 2015 [Member]
Public Utilities, General Disclosures [Line Items]
Expected pre-tax income related to abandonment costs																				1,000,000
Delmarva Power & Light Co/De [Member] | Advanced Metering Infrastructure Costs [Member]
Public Utilities, General Disclosures [Line Items]
Base rates period												15 years
Related portion of advanced metering infrastructure																																					50.00%
Delmarva Power & Light Co/De [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years												1 year
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]
Regulatory asset, amortization period, years												20 years
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															44,800,000		52,100,000
Return on equity, percentage							9.40%			9.31%	10.75%	10.80%														10.25%	9.36%	10.25%	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
Abandonment costs sought									88,000,000			43,900,000	45,000,000
Recovery period												3 years
Estimated fair value of real property acquired									2,000,000
Length transmission line																														152
Land held for future use in utility operations												2,000,000								2,000,000
Period to issue decision												180 days
Return on equity, percentage																											9.36%
Regulatory asset related to MAPP abandonment costs												19,000,000
Potomac Electric Power Co [Member] | Adjusted [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change																										44,800,000
Potomac Electric Power Co [Member] | Expected [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change							23,400,000							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] | 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%
Potomac Electric Power Co [Member] | District of Columbia [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change												23,400,000
Return on equity, percentage												9.40%
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]
Regulatory asset, amortization period, years												1 year
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]
Regulatory asset, amortization period, years												20 years
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%
Atlantic City Electric Co [Member]
Public Utilities, General Disclosures [Line Items]
Transition bond maturity, lower range												2015
Transition bond maturity, upper range												2023
Requested rate change			19,000,000																														61,700,000
Return on equity, percentage			9.75%									10.80%																					10.25%
Overall annual rate decrease as net impact of adjusting charges																																41,100,000		24,500,000	41,100,000
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 $0.4 million.
Reduction in operating income																		400,000
Atlantic City Electric Co [Member] | Minimum [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory asset, amortization period, years												1 year
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]
Regulatory asset, amortization period, years												20 years
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%
PHI [Member] | Federal Energy Regulatory Commission Return On Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
ROE determined, description												Each ten basis point reduction in the ROE would result in a reduction of Pepco's operating income of $0.6 million.
Reduction in operating income																		$ 600,000