Derivative Instruments And Hedging Activities (Net Outstanding Commodity Forward Contracts Quantities And Net Position That Did Not Qualify For Hedge Accounting) (Detail)	3 Months Ended	12 Months Ended
Mar. 31, 2013 ForwardContracts	Dec. 31, 2012 ForwardContracts
Pepco Energy Services [Member] \| Financial Transmission Rights (MWh) [Member]
Derivative [Line Items]
Commodity forward contracts	86,746	181,008
Net Position	Long	Long
Pepco Energy Services [Member] \| Electricity (MWh) [Member]
Derivative [Line Items]
Commodity forward contracts	131,640	261,240
Net Position	Long	Long
Delmarva Power & Light Co/De [Member] \| Natural Gas (MMBtu)) [Member]
Derivative [Line Items]
Commodity forward contracts	3,245,000	3,838,000
Net Position	Long	Long

Information that would enable users to understand the volume of the entity's derivative activity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44

-Subparagraph 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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