Fair Value Disclosures - Summary of Primary Unobservable Inputs Used to Determine Fair Value of Level 3 Instruments and Range of Values That Could be Used for Those Inputs (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	$ (43)	$ (43)
Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(2)	(4)
Atlantic City Electric Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(14)	(12)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(14)	(15)
Significant Unobservable Inputs (Level 3) [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument		(4)
Significant Unobservable Inputs (Level 3) [Member] | Atlantic City Electric Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(14)	(11)
Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Natural Gas Options [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument		(4)
Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(10)	(3)
Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Delmarva Power & Light Co/De [Member] | Natural Gas Options [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument		(4)
Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	$ (10)	$ (3)
Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member] | Natural Gas Options [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility Factor, Range		1.57
Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow, Discount rate		5.00%
Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member] | Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow, Discount rate	5.00%	5.00%
Minimum [Member] | Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow, Discount rate	5.00%
Minimum [Member] | Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Delmarva Power & Light Co/De [Member] | Natural Gas Options [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility Factor, Range		1.57
Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member] | Natural Gas Options [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility Factor, Range		2.00
Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow, Discount rate		9.00%
Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member] | Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow, Discount rate	9.00%	9.00%
Maximum [Member] | Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow, Discount rate	9.00%
Maximum [Member] | Derivative [Member] | Significant Unobservable Inputs (Level 3) [Member] | Delmarva Power & Light Co/De [Member] | Natural Gas Options [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility Factor, Range		2.00