Derivative Instruments and Hedging Activities - Fair Values of Derivative Instruments by Balance Sheet Location (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	$ 18	$ 3
Derivative liabilities (current liabilities)	(2)	(4)
Net derivative (liability) asset	16	(1)
Net Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	18	3
Net derivative (liability) asset	18	3
Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative assets (current assets)	18	3
Derivative liabilities (current liabilities)	(2)	(4)
Net derivative (liability) asset	16	(1)
Delmarva Power & Light Co/De [Member] | Gross Derivative Instruments [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	(2)	(4)
Delmarva Power & Light Co/De [Member] | Other Derivative Instruments [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	(2)	(4)
Effects of Cash Collateral and Netting [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	2	4
Net derivative (liability) asset	2	4
Effects of Cash Collateral and Netting [Member] | Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Derivative liabilities (current liabilities)	$ 2	$ 4