Schedule II - Valuation and Qualifying Accounts (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 38	$ 34	$ 43
Charged to Costs and Expenses	46	37	35
Charged to Other Accounts	9	5	8
Deductions	(53)	(38)	(52)
Balance at End of Period	40	38	34
Potomac Electric Power Co [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	16	13	18
Charged to Costs and Expenses	17	15	13
Charged to Other Accounts	2	1	2
Deductions	(19)	(13)	(20)
Balance at End of Period	16	16	13
Delmarva Power & Light Co/De [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	12	9	12
Charged to Costs and Expenses	13	11	11
Charged to Other Accounts	4	1	3
Deductions	(18)	(9)	(17)
Balance at End of Period	11	12	9
Atlantic City Electric Co [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	10	11	12
Charged to Costs and Expenses	12	11	12
Charged to Other Accounts	3	3	3
Deductions	(16)	(15)	(16)
Balance at End of Period	$ 9	$ 10	$ 11