Fair Value Disclosures (Fair Value Of Financial Instruments Using Unobservable Inputs (Level 3)) (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012 Derivative
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(5,416,000,000)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(501,000,000)
Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(1,024,000,000)
Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(113,000,000)
Atlantic City Electric Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(1,379,000,000)
Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(129,000,000)
Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(12,000,000)
Derivative [Member] | Fair Value, 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	(10,000,000)
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Minimum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	0.69
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Maximum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	2.78
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity Contract [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(1,000,000)
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity Contract [Member] | Minimum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow Discount rate	5.00%
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity Contract [Member] | Maximum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow Discount rate	9.00%
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Physical Basis [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(1,000,000)
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Physical Basis [Member] | Minimum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Congestion adder, range	(0.04)
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Physical Basis [Member] | Maximum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Congestion adder, range	0.72
Derivative [Member] | Delmarva Power & Light Co/De [Member] | Fair Value, 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	(10,000,000)
Derivative [Member] | Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Minimum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	0.69
Derivative [Member] | Delmarva Power & Light Co/De [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Maximum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	2.78
Derivative [Member] | Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity Contract [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(1,000,000)
Derivative [Member] | Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity Contract [Member] | Minimum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow Discount rate	5.00%
Derivative [Member] | Atlantic City Electric Co [Member] | Fair Value, Inputs, Level 3 [Member] | Capacity Contract [Member] | Maximum [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discounted cash flow Discount rate	9.00%