Schedule I - Condensed Financial Information of Parent Company - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Ownership percentage of significant subsidiaries	100.00%
Ratio of equity to total capitalization	30.00%
Retained earnings	$ 617	$ 565
Restricted net assets for consolidated subsidiaries	2,633
Surety Bond [Member]
Condensed Financial Statements, Captions [Line Items]
Guarantee obligations amount	56
Pepco Energy Services [Member] \| Performance Guarantee [Member]
Condensed Financial Statements, Captions [Line Items]
Guarantee obligations amount	269
Pepco Energy Services [Member] \| Surety Bond [Member]
Condensed Financial Statements, Captions [Line Items]
Guarantee obligations amount	177
Potomac Capital Investment Corporation (PCI) [Member]
Condensed Financial Statements, Captions [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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

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