Debt - Components of Short-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Short-term debt	$ 1,063	$ 729
Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	210	211
Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	5	127
Potomac Electric Power Co [Member]
Short-term Debt [Line Items]
Short-term debt	64	104
Term Loan [Member]
Short-term Debt [Line Items]
Short-term debt	300
Commercial Paper [Member]
Short-term Debt [Line Items]
Short-term debt	658	624
Commercial Paper [Member] | Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	105	106
Commercial Paper [Member] | Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	5	127
Commercial Paper [Member] | Potomac Electric Power Co [Member]
Short-term Debt [Line Items]
Short-term debt	64	104
Variable Rate Demand Bonds [Member]
Short-term Debt [Line Items]
Short-term debt	105	105
Variable Rate Demand Bonds [Member] | Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	$ 105	$ 105