Energy purchase maximum to be purchased

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Increase (Decrease) In Income (Loss) From Discontinued Operations Before Tax

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Incremental Storm Costs

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Long-term Contract for Purchase of Electric Power, Megawatts

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Maximum Generation Capacity, After Reduction

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Net power purchases with non-utility generators.

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Number of purchase power agreements

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O and M storm repair work.

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- Definition

Obligated purchase amount of energy produced at the facility

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- Definition

Power Of Fuel Cell Facility

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Reg assets storm repair work.

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Significant cost capital expenditures

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Term Of Agreement

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Sum of the carrying values as of the balance sheet date of liabilities incurred and payable to vendors for goods and services received, and other costs not separately disclosed in the balance sheet that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered.

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Cost of electricity purchased as well as fuel used to generate electricity used in operations and sold during the reporting period.

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Revenue from the bulk transport of high voltage power, typically over longer distances, between generating plants and distribution systems.

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-Name Accounting Standards Codification

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-Subparagraph (SX 210.5-03.1(b))

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The amount of excise and sales taxes included in sales and revenues, which are then deducted as a cost of sales. Includes excise taxes, which are applied to specific types of transactions or items (such as gasoline or alcohol); and sales, use and value added taxes, which are applied to a broad class of revenue-producing transactions involving a wide range of goods and services.

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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-Name Accounting Standards Codification

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The increase (decrease) during the period in the carrying amount of accrued known and estimated losses incurred for which no insurance coverage exists, and for which a claim has been made or is probable of being asserted, typically arising from workmen's' compensation-type of incidents and personal injury to nonemployees from accidents on the entity's property.

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The noncurrent portion of the amount recognized for uncertain tax positions as of the balance sheet date.

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The amount of a reclassification adjustment made to prior period financial statement amounts.

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The amount of operating expenses for the period that are associated with the utility's normal revenue producing operation; including selling, general, and administrative expenses, costs incurred for routine plant repairs and maintenance, and operations.

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Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended		12 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended			9 Months Ended					3 Months Ended		9 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Hurricane Irene [Member]	Sep. 30, 2011 Delmarva Power & Light Co/De [Member] Maximum [Member] mW	Sep. 30, 2011 Delmarva Power & Light Co/De [Member] Minimum [Member] mW	Sep. 30, 2011 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2010 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2011 Delmarva Power & Light Co/De [Member] Wind PPA [Member] mW	Sep. 30, 2010 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2011 Delmarva Power & Light Co/De [Member] Solar PPA [Member] mW	Sep. 30, 2011 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2010 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2011 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2010 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2011 Delmarva Power & Light Co/De [Member]	Sep. 30, 2010 Delmarva Power & Light Co/De [Member]	Sep. 30, 2011 Delmarva Power & Light Co/De [Member]	Sep. 30, 2010 Delmarva Power & Light Co/De [Member]	Aug. 19, 2011 Delmarva Power & Light Co/De [Member]	Dec. 31, 2010 Delmarva Power & Light Co/De [Member]	Sep. 30, 2011 Atlantic City Electric Co [Member]	Sep. 30, 2010 Atlantic City Electric Co [Member]	Mar. 31, 2010 Atlantic City Electric Co [Member]	Sep. 30, 2011 Atlantic City Electric Co [Member]	Sep. 30, 2010 Atlantic City Electric Co [Member]	Dec. 31, 2009 Atlantic City Electric Co [Member]	Dec. 31, 2008 Atlantic City Electric Co [Member]	Dec. 31, 2007 Atlantic City Electric Co [Member]	Sep. 30, 2011 Potomac Electric Power Co [Member]	Sep. 30, 2010 Potomac Electric Power Co [Member]	Sep. 30, 2011 Potomac Electric Power Co [Member]	Sep. 30, 2010 Potomac Electric Power Co [Member]	Dec. 31, 2010 Potomac Electric Power Co [Member]
Incremental storm costs					$ 31			$ 47
Other operation and maintenance	239			228	682	636		30												69	65	181	191			61	54		167	151				111	93	313	252
Capital expenditures								17
Electrical transmission revenue		(3)					8
Reduction in self-insurance reserves for general and auto liability claims		5
Number of purchase power agreements													3		1														3
Net power purchases with non-utility generators																57	82	169	222
Reg assets storm repair work					24
O & M storm repair work					6
Purchased energy	943			1,319	2,747	3,683					3	2	12	8		55	74	159	203
Megawatts received from power purchase agreements (PPAs)													328		10
Energy purchase maximum to be purchased													50.25		40
Term of agreement, years															20							20
Accrued payments																				1		1
Power of fuel cell facility																								30
Maximum capacity after reduction, in megawatts									60	38
Obligated purchase amount of energy produced at the facility															70.00%
Taxes included in gross revenues	111			118	302	280
Increase in revenue and pre-tax earnings			2
Reclassification adjustment				7		1														1		9						6							5	1	5
Uncertain and effectively settled tax positions	49				49		148													14		14			24						2	3	1	71		71		52
Equity ownership owned																										100.00%			100.00%
Increase in net loss from discontinued operations				$ 7