Derivative Instruments And Hedging Activities (Fair Value Of Derivative Instruments By Balance Sheet Location) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Derivative assets (current assets)			$ 1
Derivative assets (non-current assets)	8		8
Total Derivative assets	200		113
Derivative liabilities (current liabilities)	(2)		(7)
Derivative liabilities (non-current liabilities)	(11)		(11)
Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Total Derivative assets	4		3
Derivative liabilities (current liabilities)			(4)
Derivatives Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	(2)	[1]	(5)	[1]
Total Derivative liabilities	(2)	[1]	(5)	[1]
Net Derivative (liability) asset	(2)	[1]	(5)	[1]
Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1		1
Derivative assets (non-current assets)	8		8
Total Derivative assets	9		9
Derivative liabilities (current liabilities)	(2)		(8)
Derivative liabilities (non-current liabilities)	(11)		(11)
Total Derivative liabilities	(13)		(19)
Net Derivative (liability) asset	(4)		(10)
Other Derivative Instruments [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative assets (current assets)	1
Total Derivative assets	1
Derivative liabilities (current liabilities)			(4)
Total Derivative liabilities			(4)
Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1		1
Derivative assets (non-current assets)	8		8
Total Derivative assets	9		9
Derivative liabilities (current liabilities)	(4)		(13)
Derivative liabilities (non-current liabilities)	(11)		(11)
Total Derivative liabilities	(15)		(24)
Net Derivative (liability) asset	(6)		(15)
Gross Derivative Instruments [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative assets (current assets)	1
Total Derivative assets	1
Derivative liabilities (current liabilities)			(4)
Total Derivative liabilities			(4)
Effects Of Cash Collateral And Netting [Member]
Derivative [Line Items]
Derivative assets (current assets)	(1)
Total Derivative assets	(1)
Derivative liabilities (current liabilities)	2		6
Total Derivative liabilities	2		6
Net Derivative (liability) asset	1		6
Effects Of Cash Collateral And Netting [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative assets (current assets)	(1)
Total Derivative assets	(1)
Net Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)			1
Derivative assets (non-current assets)	8		8
Total Derivative assets	8		9
Derivative liabilities (current liabilities)	(2)		(7)
Derivative liabilities (non-current liabilities)	(11)		(11)
Total Derivative liabilities	(13)		(18)
Net Derivative (liability) asset	(5)		(9)
Net Derivative Instruments [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)			(4)
Total Derivative liabilities			$ (4)

[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.