Derivative Instruments and Hedging Activities - Fair Values of Derivative Instruments by Balance Sheet Location (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	$ 3	$ 1
Total Derivative asset	3	1
Net Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	3
Total Derivative asset	3
Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	3	1
Total Derivative asset	3	1
Delmarva Power & Light Co/De [Member] | Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)		1
Total Derivative asset		1
Delmarva Power & Light Co/De [Member] | Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)		1
Total Derivative asset		1
Effects of Cash Collateral and Netting [Member]
Derivative [Line Items]
Derivative assets (current assets)		(1)
Total Derivative asset		(1)
Effects of Cash Collateral and Netting [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative assets (current assets)		(1)
Total Derivative asset		$ (1)