Fair Value Disclosures (Fair Value Of Financial Liabilities Measured On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	$ 5,004	[1]	$ 4,577
Transition Bonds issued by ACE Funding, Fair Value	341	[2]	380
Long-term Project Funding, Fair Value	13		15
Total Liabilities, Fair Value	5,358
Long-Term Debt, Carrying Amount	4,177		3,867
Transition Bonds issued by ACE Funding, Carrying Amount	295		332
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	204	[1]
Total Liabilities, Fair Value	204
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	4,313	[1]
Transition Bonds issued by ACE Funding, Fair Value	341	[2]
Total Liabilities, Fair Value	4,654
Significant Unobservable 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	13
Total Liabilities, Fair Value	500
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,160	[3]	1,943
Total Liabilities, Fair Value	2,160
Long-Term Debt, Carrying Amount	1,701		1,540
Potomac Electric Power Co [Member] | Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	204	[3]
Total Liabilities, Fair Value	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	1,956	[3]
Total Liabilities, Fair Value	1,956
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	990	[4]	834
Total Liabilities, Fair Value	990
Long-Term Debt, Carrying Amount	917		765
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	877	[4]
Total Liabilities, Fair Value	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	113	[4]
Total Liabilities, Fair Value	113
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,016	[5]	1,003
Transition Bonds issued by ACE Funding, Fair Value	341	[2]	380
Total Liabilities, Fair Value	1,357
Long-Term Debt, Carrying Amount	829		832
Transition Bonds issued by ACE Funding, Carrying Amount	295		332
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	884	[5]
Transition Bonds issued by ACE Funding, Fair Value	341	[2]
Total Liabilities, Fair Value	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	132	[5]
Total Liabilities, Fair Value	$ 132

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

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

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

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

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