Regulatory Matters - Schedule of Current Base Rate Increase Requisition to Increase Annual Revenue (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	6 Months Ended	1 Months Ended
Jul. 12, 2013 Subsequent Event [Member]	Jun. 30, 2013 Delmarva Power Light Co Electric [Member] MD [Member]	Jul. 17, 2013 Delmarva Power Light Co Electric [Member] MD [Member] Subsequent Event [Member]
Regulatory Matters [Line Items]
Requested rate change		$ 22.8	$ 15.0
Return on equity, percentage	9.36%	10.25%	9.81%

Amount of public utility's requested rate increase (decrease) with regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration