Regulatory Matters (Narrative) (Detail) (USD $)	1 Months Ended				3 Months Ended		1 Months Ended				1 Months Ended					3 Months Ended	12 Months Ended				1 Months Ended			3 Months Ended	12 Months Ended		1 Months Ended	3 Months Ended	1 Months Ended		1 Months Ended			1 Months Ended			1 Months Ended										3 Months Ended	12 Months Ended		0 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended		3 Months Ended	1 Months Ended			1 Months Ended				3 Months Ended		1 Months Ended			3 Months Ended	1 Months Ended
	Mar. 29, 2013	Mar. 31, 2013	Dec. 31, 2012	Aug. 31, 2012	Mar. 31, 2013	Apr. 30, 2012 MW	Sep. 30, 2012 Expected [Member]	Mar. 31, 2013 Phi [Member]	Apr. 30, 2012 Maximum [Member] MW	Apr. 30, 2012 Minimum [Member] MW	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]	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]	Mar. 31, 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]	Mar. 31, 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]	Feb. 28, 2013 Potomac Electric Power Co [Member] Maximum [Member]	Apr. 30, 2012 Potomac Electric Power Co [Member] Maximum [Member] MW	Mar. 31, 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]	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. 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]	Nov. 30, 2012 Delmarva Power & Light Co/De [Member]	Aug. 31, 2012 Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Delmarva Power & Light Co/De [Member]	Nov. 01, 2008 Delmarva Power & Light Co/De [Member]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] MW	Jun. 01, 2013 Delmarva Power & Light Co/De [Member] Subsequent Event [Member]	Jun. 01, 2013 Delmarva Power & Light Co/De [Member] Subsequent Event [Member]	Mar. 31, 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]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member] Federal Energy Regulatory Commission Return On Equity Complaint [Member]	Feb. 28, 2013 Delmarva Power & Light Co/De [Member] Maximum [Member]	Apr. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] MW	Mar. 31, 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]	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]	Mar. 31, 2013 Atlantic City Electric Co [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	Feb. 28, 2012 Atlantic City Electric Co [Member]	Mar. 31, 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]	Mar. 31, 2013 Atlantic City Electric Co [Member] Federal Energy Regulatory Commission Return On Equity Complaint [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]
Regulatory Matters [Line Items]
Effect of proposed change on gas cost rate				22.30%																																								22.30%
Requested rate change	$ 22,800,000				$ 260,300,000						$ 52,100,000		$ 60,800,000	$ 18,100,000								$ 60,800,000	$ 18,100,000		$ 68,400,000	$ 66,200,000												$ 22,800,000	$ 42,000,000			$ 12,200,000			$ 31,800,000
Return on equity, percentage	10.25%										10.25%		10.25%	9.31%		10.80%		10.75%									8.70%	11.30%			12.80%			10.33%	10.80%		6.78%	10.25%	10.25%			10.25%	9.75%		10.75%		10.80%						8.70%	11.30%	12.80%			10.33%	10.80%		6.78%		10.25%		10.80%				8.70%	11.30%	10.33%	6.78%
Contingent rate increase																																											22,000,000		24,800,000
Rate increase implemented																																								2,500,000	2,500,000		22,000,000		24,800,000					2,500,000	2,500,000
Surcharge for recovery of costs							10,200,000																	192,000,000																												10,200,000
Proposed incentive for meeting enhanced reliability goals																								1,000,000																												500,000					500,000
Credit to customers																																	1,000,000																								500,000
Requested rate change, net																																																															70,400,000				72,100,000	1,700,000
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
New power plant output						661			700	650										661												700				650													661							700				650
Capital expenditure			102,000,000														64,000,000																															38,000,000
Recovery			88,000,000
Basis point																50.00%			200.00%																				50.00%	200.00%							50.00%															50.00%			50.00%
Denied recovery amount		2,000,000													1,000,000	1,000,000													2,000,000																	1,000,000	1,000,000
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					2,000,000				3,000,000					3,000,000													2,000,000
Capital expenditure reclassified to regulatory asset			88,000,000									50,000,000					50,000,000																									38,000,000						38,000,000
Regulatory asset		84,000,000			84,000,000											47,000,000																							37,000,000								37,000,000
Amount sought to be recovered																	$ 50,000,000