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