Fair Value Disclosures - Fair Value of Financial Liabilities Measured on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	$ 4,953	$ 5,004
Transition Bonds issued by ACE Funding, Fair Value	299	341
Long-term project funding, Fair Value	12	13
Financial Instrument, Fair Value	5,264	5,358
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
Transition Bonds issued by ACE Funding, Fair Value
Long-term project funding, Fair Value
Financial Instrument, Fair Value
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	4,387	4,517
Transition Bonds issued by ACE Funding, Fair Value	299	341
Long-term project funding, Fair Value
Financial Instrument, Fair Value	4,686	4,858
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	566	487
Transition Bonds issued by ACE Funding, Fair Value
Long-term project funding, Fair Value	12	13
Financial Instrument, Fair Value	578	500
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,237	2,160
Financial Instrument, Fair Value	2,237	2,160
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
Financial Instrument, Fair Value
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	2,237	2,160
Financial Instrument, Fair Value	2,237	2,160
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value
Financial Instrument, Fair Value
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	928	990
Financial Instrument, Fair Value	928	990
Delmarva Power & Light Co/De [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
Financial Instrument, Fair Value
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	817	877
Financial Instrument, Fair Value	817	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	111	113
Financial Instrument, Fair Value	111	113
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	978	1,016
Transition Bonds issued by ACE Funding, Fair Value	299	341
Financial Instrument, Fair Value	1,277	1,357
Atlantic City Electric 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
Transition Bonds issued by ACE Funding, Fair Value
Financial Instrument, 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	760	884
Transition Bonds issued by ACE Funding, Fair Value	299	341
Financial Instrument, Fair Value	1,059	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	218	132
Transition Bonds issued by ACE Funding, Fair Value
Financial Instrument, Fair Value	$ 218	$ 132