Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 40	$ 38	$ 34
Charged to Costs and Expenses	59	46	37
Charged to Other Accounts	5	9	5
Deductions	(48)	(53)	(38)
Balance at End of Period	56	40	38
Potomac Electric Power Co [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	16	16	13
Charged to Costs and Expenses	20	17	15
Charged to Other Accounts	1	2	1
Deductions	(20)	(19)	(13)
Balance at End of Period	17	16	16
Delmarva Power & Light Co/De [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	11	12	9
Charged to Costs and Expenses	20	13	11
Charged to Other Accounts	2	4	1
Deductions	(16)	(18)	(9)
Balance at End of Period	17	11	12
Atlantic City Electric Co [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	9	10	11
Charged to Costs and Expenses	18	12	11
Charged to Other Accounts	2	3	3
Deductions	(12)	(16)	(15)
Balance at End of Period	$ 17	$ 9	$ 10