Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset	$ 4		$ 4
Derivative Liability	14		14
Credit risk derivative liabilities, at fair value	0		0		4
Credit risk derivative liabilities, at fair value net	0		0		4
Net settlement amount in the event of a downgrade below investment grade	0		0		2
Additional collateral that would have to be posted in the event of an investment downgrade	0		0		2
Cash plus borrowing capacity to meet future liquidity needs	471		471		477
Derivative assets (non-current assets)	4		4		8
Derivative assets (non-current liabilities)	14		14		11
Atlantic City Electric Co [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset	4		4
Derivative Liability	14		14
Estimated percentage of New Jersey load			15.00%
Derivative assets (non-current assets)	4		4		8
Derivative assets (non-current liabilities)	14		14		11
Unrealized loss on derivatives	0	1	7	1
Atlantic City Electric Co [Member] \| Capacity (MWs) [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Commodity forward contracts	180		180		180
Delmarva Power & Light Co/De [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Credit risk derivative liabilities, at fair value	0		0		4
Credit risk derivative liabilities, at fair value net	0		0		4
Net settlement amount in the event of a downgrade below investment grade	0		0		2
Additional collateral that would have to be posted in the event of an investment downgrade	0		0		2
Cash plus borrowing capacity to meet future liquidity needs	$ 471		$ 471		$ 477

Credit risk derivative liabilities at fair value net.

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- Definition

Derivatives, forward contracts, did not qualify as a hedge.

+ References

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Estimated share of payments made received from standard offer capacity agreements.

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Net settlement amount in the event of a downgrade below investment grade.

+ References

No definition available.

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- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (e)

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Fair value of credit risk derivative liability.

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- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ 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 210.5-02.22(b))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Subparagraph b

-Article 5

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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