Regulatory Matters (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended				0 Months Ended	1 Months Ended			6 Months Ended		0 Months Ended	6 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	3 Months Ended	12 Months Ended			1 Months Ended
	Aug. 31, 2011	Apr. 12, 2012 MW	Apr. 12, 2012 Maximum [Member] MW	Apr. 12, 2012 Minimum [Member] MW	Dec. 16, 2011 Potomac Electric Power Co [Member]	Jun. 28, 2011 Potomac Electric Power Co [Member]	Jun. 29, 2011 Potomac Electric Power Co [Member]	Jul. 08, 2011 Potomac Electric Power Co [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Apr. 12, 2012 Potomac Electric Power Co [Member] MW	Dec. 16, 2011 Potomac Electric Power Co [Member] Expected [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member] Expected [Member]	Dec. 16, 2011 Potomac Electric Power Co [Member] Actual [Member]	Apr. 12, 2012 Potomac Electric Power Co [Member] Maximum [Member] MW	Apr. 12, 2012 Potomac Electric Power Co [Member] Minimum [Member] MW	Jul. 03, 2012 Delmarva Power & Light Co/De [Member]	Jan. 31, 2012 Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Delmarva Power & Light Co/De [Member]	Dec. 09, 2011 Delmarva Power & Light Co/De [Member]	Aug. 31, 2011 Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member]	Apr. 12, 2012 Delmarva Power & Light Co/De [Member] MW	Jul. 02, 2012 Delmarva Power & Light Co/De [Member] Subsequent Event [Member]	Dec. 09, 2011 Delmarva Power & Light Co/De [Member] Expected [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Expected [Member]	Dec. 09, 2011 Delmarva Power & Light Co/De [Member] Actual [Member]	Apr. 12, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] MW	Apr. 12, 2012 Delmarva Power & Light Co/De [Member] Minimum [Member] MW	Aug. 05, 2011 Atlantic City Electric Co [Member]	Mar. 31, 2012 Atlantic City Electric Co [Member]	Dec. 31, 2014 Atlantic City Electric Co [Member] Capital Expenditures [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member] Capital Expenditures [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member] Capital Expenditures [Member]	Feb. 24, 2012 Atlantic City Electric Co [Member] Maximum [Member]
Regulatory Matters [Line Items]
Effect of proposed change on gas cost rate	5.60%																			5.60%
Requested rate change								$ 42.0			$ 68.4	$ 18.1	$ 66.2					$ 31.8						$ 25.2	$ 11.3	$ 23.5			$ 90.3
Return on equity, percentage					10.75%			10.75%	9.31%									10.75%	10.75%		9.81%								10.75%
Rate increase implemented																22.3	2.5
Contingent rate increase																							29.3
Annual depreciation and amortization expenses									27.3												4.1
Recover in depreciation rates						8.8	9.7		18.5												4.3
Incremental storm restoration costs									9.9												4.6
Recovery of requested rate change									1.5
Requested rate change, net																													58.9					80.2
Base rate change related to excess depreciation																													17
Base rate change related to increase in sales and use taxes																													6.3
Base rate change related to regulatory asset recovery charge adjustment																													0.6
Estimated recoverable capital expenditures																															81	94	63
Projected deferred under-recovered balance related to non-utility generators																														113.8
Overall annual rate increase of the projected deferred under-recovered balance related to non-utility generators																														$ 55.3
New power plant output		661	700	650						661				700	650							661					700	650