Schedule I - Condensed Financial Information of Parent Company - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Parent Company Only Financial Information [Line Items]
Ownership percentage of significant subsidiaries	100.00%
Ratio of equity to total capitalization	30.00%
Retained earnings	$ 565	$ 595
Restricted net assets for consolidated subsidiaries	2,547
Surety Bond [Member]
Parent Company Only Financial Information [Line Items]
Guarantee obligations amount	53
Pepco Energy Services [Member] \| Performance Guarantee [Member]
Parent Company Only Financial Information [Line Items]
Guarantee obligations amount	336
Pepco Energy Services [Member] \| Surety Bond [Member]
Parent Company Only Financial Information [Line Items]
Guarantee obligations amount	185
Potomac Capital Investment Corporation (PCI) [Member]
Parent Company Only Financial Information [Line Items]
Guarantee obligations amount	$ 725

Minimum ratio of equity to capitalization.

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- Definition

Subsidiary, ownership percentage by parent.

+ References

No definition available.

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- Definition

Amount of restricted net assets of consolidated and unconsolidated subsidiaries as of the end of the most recently completed fiscal year.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(e)(3)(ii))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph e

-Subparagraph 3

-Article 4

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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

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- Definition

The cumulative amount of the reporting entity's undistributed earnings or deficit.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.31(a)(3))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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