Fair Value Disclosures (Estimated Fair Values Of Debt And Equity Instruments) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Long-term debt, Fair Value	$ 5,068	[1]	$ 4,577
Transition Bonds issued by ACE Funding, Fair Value	355	[2]	380
Long-term Project Funding, Fair Value	14		15
Long-Term Debt, Carrying Amount	4,177		3,867
Transition Bonds issued by ACE Funding, Carrying Amount	306		332
Long-Term Project Funding, Carrying Amount			15
Potomac Electric Power Co [Member]
Long-term debt, Fair Value	2,195	[3]	1,943
Long-Term Debt, Carrying Amount	1,701		1,540
Delmarva Power & Light Co/De [Member]
Long-term debt, Fair Value	996	[4]	834
Long-Term Debt, Carrying Amount	917		765
Atlantic City Electric Co [Member]
Long-term debt, Fair Value	1,029	[5]	1,003
Transition Bonds issued by ACE Funding, Fair Value	355	[2]	380
Long-Term Debt, Carrying Amount	829		832
Transition Bonds issued by ACE Funding, Carrying Amount	$ 306		$ 332

[1] The carrying amount for Long-term debt is $4,177 million as of September 30, 2012.

[2] The carrying amount for Transition Bonds issued by ACE Funding, including amounts due within one year, is $306 million as of September 30, 2012.

[3] The carrying amount for Long-term debt is $1,701 million as of September 30, 2012.

[4] The carrying amount for Long-term debt is $917 million as of September 30, 2012

[5] The carrying amount for Long-term debt is $829 million as of September 30, 2012.