Fair Value Disclosures (Fair Value Of Financial Liabilities Measured On A Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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
Total Liabilities, Fair Value	5,416
Long-Term Debt, Carrying Amount	4,213		3,867
Transition Bonds issued by ACE Funding, Carrying Amount	314		332
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,163	[3]	1,943
Total Liabilities, Fair Value	2,163
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	1,024	[4]	834
Total Liabilities, Fair Value	1,024
Long-Term Debt, Carrying Amount	948		765
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,017	[5]	1,003
Transition Bonds issued by ACE Funding, Fair Value	362	[2]	380
Total Liabilities, Fair Value	1,379
Long-Term Debt, Carrying Amount	832		832
Transition Bonds issued by ACE Funding, Carrying Amount	314		332
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,841	[1]
Total Liabilities, Fair Value	1,841
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	1,228	[3]
Total Liabilities, Fair Value	1,228
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	613	[4]
Total Liabilities, Fair Value	613
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,712	[1]
Transition Bonds issued by ACE Funding, Fair Value	362
Total Liabilities, Fair Value	3,074
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	935	[3]
Total Liabilities, Fair Value	935
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	298	[4]
Total Liabilities, Fair Value	298
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	888	[5]
Transition Bonds issued by ACE Funding, Fair Value	362	[2]
Total Liabilities, Fair Value	1,250
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	487	[1]
Long-term Project Funding, Fair Value	14	[2]
Total Liabilities, Fair Value	501
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	113	[4]
Total Liabilities, Fair Value	113
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	129	[5]
Total Liabilities, Fair Value	$ 129

[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.