Derivative Instruments And Hedging Activities (Net Outstanding Natural Gas Commodity Forward Contracts Not Qualified For Hedge Accounting) (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Pepco Energy Services [Member] \| Electricity (Mwh) [Member]
Net Position	Long	Long
Commodity forward contracts	814,776	1,455,800
Pepco Energy Services [Member] \| Electric Capacity (MW-Days) [Member]
Net Position	Long	Long
Commodity forward contracts	20,740	2,265
Pepco Energy Services [Member] \| Financial Transmission Rights (MWh) [Member]
Net Position	Long	Long
Commodity forward contracts	432,399	381,215
Pepco Energy Services [Member] \| Natural Gas (MMBtu) [Member]
Net Position	Long	Long
Commodity forward contracts	33,695,858	45,889,486
Delmarva Power & Light Co/De [Member] \| Natural Gas (MMBtu) [Member]
Net Position	Long	Long
Commodity forward contracts	5,433,500	7,827,635

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 1B

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959

Reference 2: 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=6935481&loc=SL5579245-113959

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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