Fair Value Disclosures (Estimated Fair Values Of Debt And Equity Instruments) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Long-Term Debt, Carrying Amount	$ 4,177		$ 3,867
Transition Bonds issued by ACE Funding, Carrying Amount	295		332
Long-Term Project Funding, Carrying Amount			15
Long-term debt, Fair Value	5,004	[1]	4,577
Transition Bonds issued by ACE Funding, Fair Value	341	[2]	380
Long-term Project Funding, Fair Value	13		15
Atlantic City Electric Co [Member]
Long-Term Debt, Carrying Amount	829		832
Transition Bonds issued by ACE Funding, Carrying Amount	295		332
Long-term debt, Fair Value	1,016	[3]	1,003
Transition Bonds issued by ACE Funding, Fair Value	341	[2]	380
Potomac Electric Power Co [Member]
Long-Term Debt, Carrying Amount	1,701		1,540
Long-Term Project Funding, Carrying Amount			1
Long-term debt, Fair Value	2,160	[4]	1,943
Delmarva Power & Light Co/De [Member]
Long-Term Debt, Carrying Amount	917		765
Long-term debt, Fair Value	$ 990	[5]	$ 834

[1] The carrying amount for Long-term debt is $4,177 million as of December 31, 2012.

[2] The carrying amount for Transition Bonds issued by ACE Funding, including amounts due within one year, is $295 million as of December 31, 2012.

[3] The carrying amount for Long-term debt is $829 million as of December 31, 2012.

[4] The carrying amount for Long-term debt is $1,701 million as of December 31, 2012.

[5] The carrying amount for Long-term debt is $917 million as of December 31, 2012.