Fair Value Disclosures - Fair Value of Financial Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	$ 5,632	$ 5,583
Transition Bonds, Fair Value	212	235
Long-term project funding, Fair Value	4	28
Total Liabilities, Fair Value	5,848	5,846
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	5,192	5,136
Transition Bonds, Fair Value	212	235
Total Liabilities, Fair Value	5,404	5,371
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	440	447
Long-term project funding, Fair Value	4	28
Total Liabilities, Fair Value	444	475
Potomac Electric Power Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	2,666	2,624
Long-term project funding, Fair Value		12
Total Liabilities, Fair Value		2,636
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	2,666	2,624
Total Liabilities, Fair Value		2,624
Potomac Electric Power Co [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term project funding, Fair Value		12
Total Liabilities, Fair Value		12
Delmarva Power & Light Co/De [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,174	1,123
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	1,069	1,016
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	105	107
Atlantic City Electric Co [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	1,013	1,035
Transition Bonds, Fair Value	212	235
Total Liabilities, Fair Value	1,225	1,270
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	881	903
Transition Bonds, Fair Value	212	235
Total Liabilities, Fair Value	1,093	1,138
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	132
Total Liabilities, Fair Value	$ 132	$ 132