Regulatory Matters - Additional Information (Detail) (USD $)	0 Months Ended			1 Months Ended							6 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended		0 Months Ended	6 Months Ended		1 Months Ended	0 Months Ended		6 Months Ended				0 Months Ended								1 Months Ended	6 Months Ended	12 Months Ended					0 Months Ended	6 Months Ended				0 Months Ended			0 Months Ended		0 Months Ended						1 Months Ended					6 Months Ended	12 Months Ended				0 Months Ended		1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended		6 Months Ended		1 Months Ended	0 Months Ended		0 Months Ended		1 Months Ended	0 Months Ended				1 Months Ended	6 Months Ended	0 Months Ended	6 Months Ended		0 Months Ended		0 Months Ended
	Apr. 02, 2014	Mar. 26, 2014	Sep. 20, 2013	Jun. 30, 2014 mi	Mar. 31, 2014	Oct. 31, 2013	Aug. 31, 2013	Dec. 31, 2012	Jul. 31, 2012	Dec. 31, 2011	Jun. 30, 2014	Dec. 31, 2013	Feb. 28, 2014	Apr. 30, 2012 MW	Dec. 04, 2011 Expected [Member]	Dec. 31, 2011 Expected [Member]	Dec. 31, 2011 Actual [Member]	Apr. 15, 2014 Scenario Forecast [Member]	Jun. 30, 2014 Advanced Metering Infrastructure Costs [Member]	Jun. 30, 2014 Advanced Metering Infrastructure Costs [Member] April 1, 2015 [Member]	Oct. 31, 2013 District of Columbia [Member] DC Undergrounding Task Force [Member]	Jul. 02, 2014 Subsequent Event [Member] Expected [Member]	Jul. 11, 2014 Subsequent Event [Member] Advanced Metering Infrastructure Costs [Member]	Jun. 30, 2014 2014 [Member]	Jun. 30, 2014 2015 [Member]	Apr. 30, 2012 Minimum [Member] MW	Apr. 30, 2012 Maximum [Member] MW	Jun. 30, 2014 Delmarva Power & Light Co/De [Member]	Oct. 08, 2013 Delmarva Power & Light Co/De [Member]	Oct. 02, 2013 Delmarva Power & Light Co/De [Member]	Sep. 20, 2013 Delmarva Power & Light Co/De [Member]	Aug. 28, 2013 Delmarva Power & Light Co/De [Member]	Jun. 01, 2013 Delmarva Power & Light Co/De [Member]	Mar. 22, 2013 Delmarva Power & Light Co/De [Member]	Apr. 02, 2012 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Jun. 30, 2014 Delmarva Power & Light Co/De [Member] mi	Dec. 31, 2013 Delmarva Power & Light Co/De [Member]	Feb. 28, 2014 Delmarva Power & Light Co/De [Member]	Oct. 08, 2013 Delmarva Power & Light Co/De [Member]	Oct. 02, 2013 Delmarva Power & Light Co/De [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] MW	Feb. 28, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Delmarva Power & Light Co/De [Member] Advanced Metering Infrastructure Costs [Member]	Jun. 30, 2014 Delmarva Power & Light Co/De [Member] Advanced Metering Infrastructure Costs [Member] April 1, 2015 [Member]	Jul. 11, 2014 Delmarva Power & Light Co/De [Member] Subsequent Event [Member] Advanced Metering Infrastructure Costs [Member]	Jun. 30, 2014 Delmarva Power & Light Co/De [Member] 2014 [Member]	Jun. 30, 2014 Delmarva Power & Light Co/De [Member] 2015 [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Minimum [Member] MW	Feb. 28, 2013 Delmarva Power & Light Co/De [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] MW	Feb. 28, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 26, 2014 Potomac Electric Power Co [Member]	Dec. 03, 2013 Potomac Electric Power Co [Member]	Jul. 12, 2013 Potomac Electric Power Co [Member]	Mar. 08, 2013 Potomac Electric Power Co [Member]	Aug. 24, 2012 Potomac Electric Power Co [Member] mi	Oct. 31, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member]	Jul. 31, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]	Jun. 30, 2014 Potomac Electric Power Co [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member]	Feb. 28, 2014 Potomac Electric Power Co [Member]	Jul. 12, 2013 Potomac Electric Power Co [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] MW	Mar. 26, 2014 Potomac Electric Power Co [Member] Expected [Member]	Dec. 04, 2013 Potomac Electric Power Co [Member] Expected [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member] Expected [Member]	Mar. 08, 2013 Potomac Electric Power Co [Member] Adjusted [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member] Actual [Member]	Apr. 15, 2014 Potomac Electric Power Co [Member] Scenario Forecast [Member]	Feb. 28, 2013 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Potomac Electric Power Co [Member] District of Columbia [Member]	Oct. 31, 2013 Potomac Electric Power Co [Member] District of Columbia [Member] DC Undergrounding Task Force [Member]	Jul. 02, 2014 Potomac Electric Power Co [Member] Subsequent Event [Member] Expected [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Minimum [Member] MW	Feb. 28, 2013 Potomac Electric Power Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] MW	Nov. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] Expected [Member]	Feb. 28, 2013 Potomac Electric Power Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Apr. 16, 2014 Atlantic City Electric Co [Member]	Mar. 14, 2014 Atlantic City Electric Co [Member]	Mar. 03, 2014 Atlantic City Electric Co [Member]	May 31, 2014 Atlantic City Electric Co [Member]	Jun. 30, 2014 Atlantic City Electric Co [Member]	Feb. 28, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Atlantic City Electric Co [Member] Minimum [Member]	Feb. 28, 2013 Atlantic City Electric Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2014 Atlantic City Electric Co [Member] Maximum [Member]	Feb. 28, 2013 Atlantic City Electric Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]
Public Utilities, General Disclosures [Line Items]
Requested rate change		$ 23,400,000	$ 39,000,000		$ 61,700,000				$ 18,100,000						$ 43,300,000	$ 68,400,000	$ 66,200,000					$ 8,750,000								$ 56,000,000	$ 39,000,000			$ 42,000,000	$ 15,100,000																				$ 44,800,000		$ 52,100,000					$ 18,100,000	$ 68,400,000						$ 23,400,000	$ 43,300,000	$ 60,800,000	$ 44,800,000	$ 66,200,000						$ 8,750,000							$ 61,700,000
Return on equity, percentage		9.40%			10.25%				9.31%	10.75%					10.25%							9.62%							9.70%					10.25%	9.70%		10.80%						8.70%	11.30%							6.78%		10.33%	9.40%	10.25%	9.36%	10.25%				10.25%	9.31%	10.75%	10.80%						10.25%					8.70%	11.30%			9.62%		6.78%			10.33%		10.25%			10.80%	8.70%	11.30%		6.78%		10.33%
Interim rate increase implemented																																	2,500,000
Additional interim rate increase implemented	15,100,000																												25,100,000
Interim rates in effect subject to refund																																								27,600,000
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
Base rates period																			2 years																										2 years
Portion of advanced metering infrastructure in percentage																				50.00%			50.00%																							50.00%	50.00%
Effect of proposed change on gas cost rate							(5.50%)																									(5.50%)
Surcharge for recovery of costs																																																																							192,000,000
Proposed incentive for meeting enhanced reliability goals																																																																							1,000,000												1,000,000
Credit to customers																																																																																			1,000,000
Requested rate change																																																								27,900,000																					23,400,000
Deferred operation and maintenance expenses																																																																			23,600,000
Period of amortized expenses																																																								5 years
Charges on cost of recovery																																																								24,000,000
Adjusted rate change																		37,400,000																																																								37,400,000
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			1,000,000		1,000,000
Basis point																																					0.50%																											0.50%																									0.50%
New power plant output														661												650	700															661								650		700																661												650		700
Undergrounding project cost						1,000,000,000																																																					1,000,000,000
Bear estimated complete project						500,000,000																																																					500,000,000
Underground project cost																					375,000,000																																																									375,000,000
Abandonment costs sought				80,500,000				88,000,000				82,000,000																								38,000,000	36,600,000	37,000,000																						50,000,000				43,900,000	45,000,000
Recovery period				3 years																																3 years																												3 years
Estimated fair value of real property acquired													8,000,000																										6,000,000																											2,000,000
Length transmission line				152																																	152																					152
Abandonment costs				46,000,000							46,000,000
Expected pre-tax income related to abandonment costs																								3,000,000	1,000,000																							3,000,000	1,000,000
Land held for future use in utility operations				8,000,000							8,000,000																										6,000,000																											2,000,000
Number of days to issue order											180 days																										180 days																											180 days
Merger agreement											The VSCC is required to rule on the application within 60 days, which may be extended by up to 120 days. On June 16, 2014, the VSCC issued an order extending the time period for issuing a decision by an additional 60 days, to October 1, 2014
Number of days to grant approval											90 days																										90 days																											90 days																									90 days
Return on equity, percentage																																																								9.36%																					9.40%
Regulatory asset related to MAPP abandonment costs																												$ 19,000,000																																				$ 27,000,000