Regulatory Matters (Schedule Of Current Base Rate Increase Requisition To Increase Annual Revenue) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	1 Months Ended			3 Months Ended	12 Months Ended	3 Months Ended					1 Months Ended	3 Months Ended
	Mar. 29, 2013	Mar. 31, 2013	Mar. 08, 2013 Potomac Electric Power Co [Member]	Nov. 30, 2012 Potomac Electric Power Co [Member]	Jul. 31, 2012 Potomac Electric Power Co [Member]	Mar. 31, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]	Mar. 31, 2013 Potomac Electric Power Co [Member] MD [Member]	Mar. 31, 2013 Potomac Electric Power Co [Member] DC [Member]	Mar. 31, 2013 Delmarva Power Light Co Gas [Member] DE [Member]	Mar. 31, 2013 Delmarva Power Light Co Electric [Member] MD [Member]	Mar. 31, 2013 Delmarva Power Light Co Electric [Member] DE [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	Mar. 31, 2013 Atlantic City Electric Co [Member]	Mar. 31, 2013 Atlantic City Electric Co [Member] NJ [Member]
Regulatory Matters [Line Items]
Requested rate change	$ 22.8	$ 260.3	$ 52.1	$ 60.8	$ 18.1			$ 60.8	$ 52.1	$ 12.2	$ 22.8	$ 42.0			$ 70.4
Return on equity, percentage	10.25%		10.25%	10.25%	9.31%	10.80%	10.75%	10.25%	10.25%	10.25%	10.25%	10.25%	10.25%	10.80%	10.25%
Initial Filing Date								Nov. 30, 2012	Mar. 08, 2013	Dec. 07, 2012	Mar. 29, 2013	Mar. 22, 2013			Jan. 04, 2013	[1]
Expected Timing of Decision								Q3-2013	Q4-2013	Q3-2013	Q4-2013	Q4-2013			Q4-2013

[1] Filed 12/11/12; updated test period to 12 months actual data on 01/04/13.