Income Taxes - Other Taxes (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	$ 123	$ 133	$ 135
Property	84us-gaap_RealEstateTaxExpense	77us-gaap_RealEstateTaxExpense	75us-gaap_RealEstateTaxExpense
County Fuel and Energy	143	153	160
Environmental, Use and Other	63	65	62
Total	413	428	432
Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	107	108	106
Property	51	45	46
County Fuel and Energy	143	153	160
Environmental, Use and Other	62	62	60
Total	363	368	372
Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery	16	15	14
Property	24	24	21
Environmental, Use and Other	2	1	1
Total	42	40	36
Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Gross Receipts/Delivery		10	14
Property	3	3	3
Environmental, Use and Other	(1)	1	1
Total	$ 2	$ 14	$ 18

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Taxes for continuing operations county fuel and energy.

+ References

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- Definition

Taxes for continuing operations environmental use and other.

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- Definition

Taxes for continuing operations gross receipts and delivery.

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- Definition

A tax based on the assessed value of real estate by the local government. The tax is usually based on the value of property (including the land).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 720

-SubTopic 30

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6419918&loc=d3e35301-107843

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- Definition

All taxes not related to income of the entity or excise or sales taxes levied on the revenue of the entity that are not reported elsewhere. These taxes could include production, real estate, personal property, and pump tax.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.9)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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