Regulatory Matters - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended	6 Months Ended			1 Months Ended						1 Months Ended								3 Months Ended	6 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended					6 Months Ended	1 Months Ended				1 Months Ended							3 Months Ended	6 Months Ended	12 Months Ended				1 Months Ended			6 Months Ended	12 Months Ended		1 Months Ended	6 Months Ended	1 Months Ended		6 Months Ended	1 Months Ended					1 Months Ended				1 Months Ended				6 Months Ended		1 Months Ended			6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended
	May 31, 2013	Dec. 31, 2012	Aug. 31, 2012	Mar. 31, 2013	Jun. 30, 2013	Apr. 30, 2012 MW	Mar. 31, 2013 Phi [Member]	Jul. 12, 2013 Subsequent Event [Member]	May 31, 2013 DC Undergrounding Task Force Member District of Columbia [Member]	Jun. 30, 2013 Maximum [Member]	Apr. 30, 2012 Maximum [Member] MW	Jun. 30, 2013 Minimum [Member]	Apr. 30, 2012 Minimum [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member]	Mar. 29, 2013 Delmarva Power & Light Co/De [Member]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member]	Feb. 28, 2013 Delmarva Power & Light Co/De [Member]	Feb. 05, 2013 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Aug. 31, 2012 Delmarva Power & Light Co/De [Member]	Nov. 01, 2008 Delmarva Power & Light Co/De [Member]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Expected [Member]	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jul. 17, 2013 Delmarva Power & Light Co/De [Member] Subsequent Event [Member]	Jul. 17, 2013 Delmarva Power & Light Co/De [Member] Subsequent Event [Member] MD [Member]	Feb. 28, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Expected [Member]	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Feb. 28, 2013 Delmarva Power & Light Co/De [Member] Minimum [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Minimum [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Minimum [Member] MW	Feb. 27, 2013 Delmarva Power & Light Co/De [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	May 31, 2013 Potomac Electric Power Co [Member]	Mar. 08, 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]	Nov. 01, 2008 Potomac Electric Power Co [Member]	Mar. 31, 2013 Potomac Electric Power Co [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]	Feb. 28, 2013 Potomac Electric Power Co [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] MW	Nov. 01, 2008 Potomac Electric Power Co [Member] Non Recoverable Rate [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member] Expected [Member]	Jul. 31, 2012 Potomac Electric Power Co [Member] Expected [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] Expected [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member] Expected [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member] Actual [Member]	Feb. 27, 2013 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Nov. 01, 2008 Potomac Electric Power Co [Member] Phi [Member]	Mar. 31, 2013 Potomac Electric Power Co [Member] Phi [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] MD [Member]	Jul. 12, 2013 Potomac Electric Power Co [Member] Subsequent Event [Member]	Feb. 28, 2013 Potomac Electric Power Co [Member] Maximum [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] Maximum [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] MW	Jun. 30, 2013 Potomac Electric Power Co [Member] Maximum [Member] Expected [Member]	Feb. 27, 2013 Potomac Electric Power Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Feb. 28, 2013 Potomac Electric Power Co [Member] Minimum [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member] Minimum [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Minimum [Member] MW	Feb. 27, 2013 Potomac Electric Power Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Mar. 31, 2013 Atlantic City Electric Co [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	Feb. 28, 2012 Atlantic City Electric Co [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] Distribution Rate [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] Recovery Charges [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member] New Jersey Settlement [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member] New Jersey Settlement [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Maximum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	Feb. 27, 2013 Atlantic City Electric Co [Member] Minimum [Member] Federal Energy Regulatory Commission Return on Equity Complaint [Member]	May 31, 2013 PHI [Member]
Regulatory Matters [Line Items]
Effect of proposed change on gas cost rate			22.30%																	22.30%
Requested rate change															$ 22,800,000	$ 42,000,000			$ 12,000,000										$ 15,000,000											$ 52,100,000		$ 60,800,000	$ 18,100,000									$ 60,800,000	$ 18,100,000		$ 68,400,000	$ 66,200,000
Return on equity, percentage								9.36%							10.25%	10.25%			10.25%				10.80%			8.70%	11.30%	9.81%	9.81%	12.80%				10.33%	10.80%			6.78%		10.25%		10.25%	9.31%			10.80%		10.75%									8.70%	11.30%				9.36%	12.80%				10.33%	10.80%			6.78%		10.25%		10.80%				8.70%	11.30%		9.75%	10.33%	6.78%
Rate increase implemented														2,500,000			2,500,000	2,500,000
Rate additional increase implemented																							8,000,000
Surcharge for recovery of costs																									10,200,000																													192,000,000
Proposed incentive for meeting enhanced reliability goals																									500,000								500,000																					1,000,000
Credit to customers																																	500,000																																	1,000,000
Deferred operation and maintenance expenses																												6,000,000																		23,600,000																23,600,000
Period of amortized expenses																												5 years																																		5 years
Charges on cost of recovery																												4,200,000																		24.0																24,000,000													67,900,000
Annual depreciation and amortization expenses																																														27,300,000		27,300,000
Requested rate change								27,800,000																				15,000,000																																	27,800,000	27,800,000
Requested rate change, net																																																																									70,400,000				72,100,000	1,700,000				25,500,000
Requested rate change, net																																																																																		25,500,000
Distribution revenue increase																																																																																		70,000,000
Capital costs																																																																																		44,200,000
Maintenance expenses																																																																																	25,800,000
Depreciation expense reduced																																																																																	8,300,000
Base rate change related to increase in sales-and-use taxes																																																																																	4,900,000
Projected deferred under-recovered balance related to non-utility generators																																																																										113,800,000		127,000,000
Overall annual rate increase of the projected deferred under-recovered balance related to non-utility generators																																																																								52,200,000		55,300,000	52,200,000
Projected deferred under recovered balance																																																																											40,800,000
Additional projected deferred under recovered balance																																																																											32,900,000
Amortization period																																																																											4 years
New power plant output						661					700		650											661								700					650													661															700					650
Aggregate derivative liability										70,000,000		55,000,000																			20,000,000					15,000,000																												50,000,000					40,000,000
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
Capital expenditure					102,000,000																		38,000,000																							64,000,000
Recovery		88,000,000
Basis point														50.00%			200.00%						50.00%																							50.00%			200.00%																										50.00%
Denied recovery amount				2,000,000																	1,000,000	1,000,000																						1,000,000	1,000,000														2,000,000
Recovery percentage																					50.00%																									50.00%					50.00%
Capital expenditure placed in service		11,000,000																																							11,000,000
Transfer of materials to inventory		3,000,000		3,000,000			2,000,000																																		3,000,000					3,000,000	3,000,000													2,000,000
Capital expenditure reclassified to regulatory asset		88,000,000																	38,000,000																						50,000,000						50,000,000
Regulatory asset					81,000,000									37,000,000									37,000,000																							44,000,000
Return on equity, percentage																																																													9.36%	9.36%
Amount sought to be recovered																																															$ 50,000,000