Derivative Instruments and Hedging Activities - Fair Value of Derivative Instruments by Balance Sheet Location (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives Designated as Hedging Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)
Total Derivative asset
Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1	1
Total Derivative asset	1	1
Net Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)
Total Derivative asset
Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1	1
Total Derivative asset	1	1
Delmarva Power & Light Co/De [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)
Total Derivative asset
Delmarva Power & Light Co/De [Member] | Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1	1
Total Derivative asset	1	1
Delmarva Power & Light Co/De [Member] | Net Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)
Total Derivative asset
Delmarva Power & Light Co/De [Member] | Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	1	1
Total Derivative asset	1	1
Effects of Cash Collateral and Netting [Member]
Derivative [Line Items]
Derivative assets (current assets)	(1)	(1)
Total Derivative asset	(1)	(1)
Effects of Cash Collateral and Netting [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative assets (current assets)	(1)	(1)
Total Derivative asset	$ (1)	$ (1)