Fair Value Disclosures (Estimated Fair Values Of Debt And Equity Instruments) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Long-term debt, Fair Value	$ 5,040	[1]	$ 4,577
Transition Bonds issued by ACE Funding, Fair Value	362		380
Long-term Project Funding, Fair Value	14	[2]	15
Long-Term Debt, Carrying Amount	4,213		3,867
Transition Bonds issued by ACE Funding, Carrying Amount	314		332
Long-Term Project Funding, Carrying Amount			15
Potomac Electric Power Co [Member]
Long-term debt, Fair Value	2,163	[3]	1,943
Long-Term Debt, Carrying Amount	1,701		1,540
Delmarva Power & Light Co/De [Member]
Long-term debt, Fair Value	1,024	[4]	834
Long-Term Debt, Carrying Amount	948		765
Atlantic City Electric Co [Member]
Long-term debt, Fair Value	1,017	[5]	1,003
Transition Bonds issued by ACE Funding, Fair Value	362	[2]	380
Long-Term Debt, Carrying Amount	832		832
Transition Bonds issued by ACE Funding, Carrying Amount	$ 314		$ 332

[1] The carrying amount for Long-term debt is $4,213 million as of June 30, 2012.

[2] The carrying amount for Transition Bonds issued by ACE Funding, including amounts due within one year, is $314 million as of June 30, 2012.

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

[4] The carrying amount for Long-term debt is $948 million as of June 30, 2012.

[5] The carrying amount for Long-term debt is $832 million as of June 30, 2012.