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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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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- Definition

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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- Definition

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 within one year or 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

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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Derivative Instruments and Hedging Activities - Fair Value of Derivative Instruments by Balance Sheet Location (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Other Derivative Instruments [Member]	Dec. 31, 2012 Other Derivative Instruments [Member]	Sep. 30, 2013 Other Derivative Instruments [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Other Derivative Instruments [Member] Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Gross Derivative Instruments [Member]	Dec. 31, 2012 Gross Derivative Instruments [Member]	Sep. 30, 2013 Gross Derivative Instruments [Member] Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Gross Derivative Instruments [Member] Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Effects of Cash Collateral and Netting [Member]	Sep. 30, 2013 Effects of Cash Collateral and Netting [Member] Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Net Derivative Instruments [Member]	Dec. 31, 2012 Net Derivative Instruments [Member]	Dec. 31, 2012 Net Derivative Instruments [Member] Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative assets (non-current assets)	$ 4	$ 8		$ 4	$ 8			$ 4	$ 8					$ 4	$ 8
Total Derivative assets	4			4	8			4	8					4	8
Derivative liabilities (current liabilities)		(4)	(4)	(1)	(4)	(1)	(4)	(1)	(4)	(1)	(4)	1	1		(4)	(4)
Derivative liabilities (non-current liabilities)	(14)	(11)		(14)	(11)			(14)	(11)					(14)	(11)
Total Derivative liabilities	(14)			(15)	(15)	(1)	(4)	(15)	(15)	(1)	(4)	1	1	(14)	(15)	(4)
Net Derivative (liability) asset				$ (11)	$ (7)			$ (11)	$ (7)			$ 1		$ (10)	$ (7)