Regulatory Matters - Schedule of Current Base Rate Approval to Increase Annual Revenue (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Jul. 12, 2013 Potomac Electric Power Co [Member]	Mar. 31, 2014 Potomac Electric Power Co [Member] District of Columbia [Member]	Mar. 31, 2014 Delmarva Power Light Co Electric [Member] DE [Member]
Regulatory Matters [Line Items]
Approved Revenue Requirement Increase	$ 27.9	$ 23.4	$ 15.1
Approved Return on Equity	9.36%	9.40%	9.70%
Completion Date		Mar. 26, 2014	Apr. 02, 2014
Rate Effective Date		Apr. 16, 2014	May 01, 2014