Fair Value Disclosures (Fair Value Of Financial Liabilities Measured On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	$ 5,194	[1]	$ 5,004	[2]
Transition Bonds issued by ACE Funding, Fair Value	327	[3]	341	[4]
Long-term project funding, Fair Value	13		13
Total Liabilities, Fair Value	5,534		5,358
Long-term debt, Carrying Amount	4,426		4,177
Transition Bonds issued by ACE Funding, Carrying Amount	285		295
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	386	[1]	204	[2]
Total Liabilities, Fair Value	386		204
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	4,326	[1]	4,313	[2]
Transition Bonds issued by ACE Funding, Fair Value	327	[3]	341	[4]
Total Liabilities, Fair Value	4,653		4,654
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	482	[1]	487	[2]
Long-term project funding, Fair Value	13		13
Total Liabilities, Fair Value	495		500
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,387	[5]	2,160	[6]
Total Liabilities, Fair Value	2,387		2,160
Long-term debt, Carrying Amount	1,951		1,701
Potomac Electric Power Co [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	371	[5]	204	[6]
Total Liabilities, Fair Value	371		204
Potomac Electric Power Co [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,016	[5]	1,956	[6]
Total Liabilities, Fair Value	2,016		1,956
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	968	[7]	990	[8]
Total Liabilities, Fair Value	968		990
Long-term debt, Carrying Amount	917		917
Delmarva Power & Light Co/De [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	15	[7]
Total Liabilities, Fair Value	15
Delmarva Power & Light Co/De [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	841	[7]	877	[8]
Total Liabilities, Fair Value	841		877
Delmarva Power & Light Co/De [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	112	[7]	113	[8]
Total Liabilities, Fair Value	112		113
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,007	[9]	1,016	[10]
Transition Bonds issued by ACE Funding, Fair Value	327	[3]	341	[4]
Total Liabilities, Fair Value	1,334		1,357
Long-term debt, Carrying Amount	829		829
Transition Bonds issued by ACE Funding, Carrying Amount	285		295
Atlantic City Electric Co [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value		[9]		[10]
Total Liabilities, Fair Value
Atlantic City Electric Co [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	877	[9]	884	[10]
Transition Bonds issued by ACE Funding, Fair Value	327	[3]	341	[4]
Total Liabilities, Fair Value	1,204		1,225
Atlantic City Electric Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	130	[9]	132	[10]
Total Liabilities, Fair Value	$ 130		$ 132

[1] The carrying amount for Long-term debt is $4,426 million as of March 31, 2013.

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

[3] The carrying amount for Transition Bonds issued by ACE Funding, including amounts due within one year, is $285 million as of March 31, 2013.

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

[5] The carrying amount for Long-term debt is $1,951 million as of March 31, 2013.

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

[7] The carrying amount for Long-term debt is $917 million as of March 31, 2013.

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

[9] The carrying amount for Long-term debt is $829 million as of March 31, 2013.

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