Derivative Instruments And Hedging Activities (Fair Value Of Derivative Instruments by Balance Sheet Location) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Derivative [Line Items]
Derivative assets (current assets)	$ 1		$ 5
Derivative assets (non-current assets)	8
Total Derivative assets	113		192
Derivative liabilities (current liabilities)	(7)		(26)
Derivative liabilities (non-current liabilities)	(11)		(6)
Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Total Derivative assets	3		3
Derivative liabilities (current liabilities)	(4)		(12)
Derivative liabilities (non-current liabilities)			(3)
Derivatives Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)			17	[1]
Total Derivative assets			17	[1]
Derivative liabilities (current liabilities)	(10)	[2]	(55)	[1]
Derivative liabilities (non-current liabilities)	(1)	[2]	(11)	[1]
Total Derivative liabilities	(11)	[2]	(66)	[1]
Net Derivative (liability) asset	(11)	[2]	(49)	[1]
Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1		6
Derivative assets (non-current assets)	8		1
Total Derivative assets	9		7
Derivative liabilities (current liabilities)	(13)		(48)
Derivative liabilities (non-current liabilities)	(12)		(10)
Total Derivative liabilities	(25)		(58)
Net Derivative (liability) asset	(16)		(51)
Other Derivative Instruments [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	(4)		(14)
Derivative liabilities (non-current liabilities)			(3)
Total Derivative liabilities	(4)		(17)
Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1		23
Derivative assets (non-current assets)	8		1
Total Derivative assets	9		24
Derivative liabilities (current liabilities)	(23)		(103)
Derivative liabilities (non-current liabilities)	(13)		(21)
Total Derivative liabilities	(36)		(124)
Net Derivative (liability) asset	(27)		(100)
Gross Derivative Instruments [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	(4)		(14)
Derivative liabilities (non-current liabilities)			(3)
Total Derivative liabilities	(4)		(17)
Effects Of Cash Collateral And Netting [Member]
Derivative [Line Items]
Derivative assets (current assets)			(18)
Derivative assets (non-current assets)			(1)
Total Derivative assets			(19)
Derivative liabilities (current liabilities)	16		77
Derivative liabilities (non-current liabilities)	2		15
Total Derivative liabilities	18		92
Net Derivative (liability) asset	18		73
Effects Of Cash Collateral And Netting [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)			2
Total Derivative liabilities			2
Net Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1		5
Derivative assets (non-current assets)	8
Total Derivative assets	9		5
Derivative liabilities (current liabilities)	(7)		(26)
Derivative liabilities (non-current liabilities)	(11)		(6)
Total Derivative liabilities	(18)		(32)
Net Derivative (liability) asset	(9)		(27)
Net Derivative Instruments [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	(4)		(12)
Derivative liabilities (non-current liabilities)			(3)
Total Derivative liabilities	$ (4)		$ (15)

[1] Amounts included in Derivatives Designated as Hedging Instruments primarily consist of derivatives that were designated as cash flow hedges prior to Pepco Energy Services' election to discontinue cash flow hedge accounting for these derivatives.

[2] Represents wholesale electricity futures and swaps that are used mainly as part of Pepco Energy Services' retail energy supply business.