Fair Value Disclosures (Fair Value Of Financial Liabilities Measured On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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
Total Liabilities, Fair Value	5,437
Long-Term Debt, Carrying Amount	4,177		3,867
Transition Bonds issued by ACE Funding, Carrying Amount	306		332
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,195	[3]	1,943
Total Liabilities, Fair Value	2,195
Long-Term Debt, Carrying Amount	1,701		1,540
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	996	[4]	834
Total Liabilities, Fair Value	996
Long-Term Debt, Carrying Amount	917		765
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,029	[5]	1,003
Transition Bonds issued by ACE Funding, Fair Value	355	[2]	380
Total Liabilities, Fair Value	1,384
Long-Term Debt, Carrying Amount	829		832
Transition Bonds issued by ACE Funding, Carrying Amount	306		332
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	990	[1]
Total Liabilities, Fair Value	990
Fair Value, Inputs, Level 1 [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	712	[3]
Total Liabilities, Fair Value	712
Fair Value, Inputs, Level 1 [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	278	[4]
Total Liabilities, Fair Value	278
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	3,584	[1]
Transition Bonds issued by ACE Funding, Fair Value	355	[2]
Total Liabilities, Fair Value	3,939
Fair Value, Inputs, Level 2 [Member] | Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,483	[3]
Total Liabilities, Fair Value	1,483
Fair Value, Inputs, Level 2 [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	603	[4]
Total Liabilities, Fair Value	603
Fair Value, Inputs, Level 2 [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	894	[5]
Transition Bonds issued by ACE Funding, Fair Value	355	[2]
Total Liabilities, Fair Value	1,249
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	494	[1]
Long-term Project Funding, Fair Value	14
Total Liabilities, Fair Value	508
Fair Value, Inputs, Level 3 [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	115	[4]
Total Liabilities, Fair Value	115
Fair Value, Inputs, Level 3 [Member] | Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	135	[5]
Total Liabilities, Fair Value	$ 135

[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.