Debt - Components of Short-Term Debt (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Short-term debt	$ 565	$ 965
Potomac Electric Power Co [Member]
Short-term Debt [Line Items]
Short-term debt	151	231
Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	252	137
Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	138	133
Commercial Paper [Member]
Short-term Debt [Line Items]
Short-term debt	442	637
Commercial Paper [Member] | Potomac Electric Power Co [Member]
Short-term Debt [Line Items]
Short-term debt	151	231
Commercial Paper [Member] | Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	147	32
Commercial Paper [Member] | Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	120	110
Variable Rate Demand Bonds [Member]
Short-term Debt [Line Items]
Short-term debt	123	128
Variable Rate Demand Bonds [Member] | Delmarva Power & Light Co/De [Member]
Short-term Debt [Line Items]
Short-term debt	105	105
Variable Rate Demand Bonds [Member] | Atlantic City Electric Co [Member]
Short-term Debt [Line Items]
Short-term debt	18	23
Term Loan Agreement [Member]
Short-term Debt [Line Items]
Short-term debt		$ 200