Regulatory Matters - Schedule of Current Base Rate Approval to Increase Annual Revenue (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended
	Jul. 12, 2013	Dec. 31, 2014
Potomac Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Approved Revenue Requirement Increase	$ 27.9
Approved Return on Equity	9.36%
Potomac Electric Power Co [Member] | District of Columbia [Member]
Public Utilities, General Disclosures [Line Items]
Approved Revenue Requirement Increase		23.4
Approved Return on Equity		9.40%
Completion Date		Mar. 26, 2014
Rate Effective Date		Apr. 16, 2014
Potomac Electric Power Co [Member] | MD [Member]
Public Utilities, General Disclosures [Line Items]
Approved Revenue Requirement Increase		8.8
Approved Return on Equity		9.62%
Completion Date		Jul. 02, 2014
Rate Effective Date		Jul. 04, 2014
Delmarva Power Light Co Electric [Member] | DE [Member]
Public Utilities, General Disclosures [Line Items]
Approved Revenue Requirement Increase		15.1
Approved Return on Equity		9.70%
Completion Date		Aug. 05, 2014
Rate Effective Date		May 01, 2014
Atlantic City Electric Co [Member] | NJ [Member]
Public Utilities, General Disclosures [Line Items]
Approved Revenue Requirement Increase		$ 19.0
Approved Return on Equity		9.75%
Completion Date		Aug. 20, 2014
Rate Effective Date		Sep. 01, 2014