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