Regulatory Matters - Schedule of Current Base Rate Increase Requisition to Increase Annual Revenue (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended			9 Months Ended	12 Months Ended
	Mar. 08, 2013	Nov. 30, 2012	Jul. 31, 2012	Sep. 30, 2013	Dec. 31, 2011
Potomac Electric Power Co [Member]
Regulatory Matters [Line Items]
Requested rate change	$ 44.1	$ 60.8	$ 18.1
Return on equity, percentage	10.25%	10.25%	9.31%	10.80%	10.75%
Potomac Electric Power Co [Member] | DC [Member]
Regulatory Matters [Line Items]
Requested rate change				44.1
Return on equity, percentage				10.25%
Initial Filing Date				Mar. 08, 2013
Expected Timing of Decision				Q1-2014
Delmarva Power Light Co Electric [Member] | DE [Member]
Regulatory Matters [Line Items]
Requested rate change				$ 39.0
Return on equity, percentage				10.25%
Initial Filing Date				Mar. 22, 2013
Expected Timing of Decision				Q1-2014