Schedule II - Valuation And Qualifying Accounts (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 49		$ 51		$ 44
Charged to Costs and Expenses	32		45		53
Charged to Other Accounts	8	[1]	8	[1]	6	[1]
Deductions	(53)	[2]	(55)	[2]	(52)	[2]
Balance at End of Period	36		49		51
Potomac Electric Power Co [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	18		20		17
Charged to Costs and Expenses	13		21		26
Charged to Other Accounts	2	[1]	2	[1]	1	[1]
Deductions	(20)	[2]	(25)	[2]	(24)	[2]
Balance at End of Period	13		18		20
Delmarva Power & Light Co/De [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	12		13		12
Charged to Costs and Expenses	11		11		13
Charged to Other Accounts	3	[1]	3	[1]	3	[1]
Deductions	(17)	[2]	(15)	[2]	(15)	[2]
Balance at End of Period	9		12		13
Atlantic City Electric Co [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	12		11		7
Charged to Costs and Expenses	12		13		13
Charged to Other Accounts	3	[1]	3	[1]	2	[1]
Deductions	(16)	[2]	(15)	[2]	(11)	[2]
Balance at End of Period	$ 11		$ 12		$ 11

[1] Collection of accounts previously written off.

[2] Uncollectible accounts written off.