Fair Value Disclosures (Fair Value Of Financial Instruments Using Unobservable Inputs (Level 3)) (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012 Derivative
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	5,437,000,000
Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	996,000,000
Atlantic City Electric Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	1,384,000,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	508,000,000
Fair Value, 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	115,000,000
Fair Value, 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	135,000,000
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	(7,000,000)
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value of financial instrument	(7,000,000)
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	0.82
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Minimum [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	0.82
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	2.76
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Options [Member] | Maximum [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Volatility factor, range	2.76
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] | Atlantic City Electric Co [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] | Minimum [Member] | Atlantic City Electric Co [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] | Capacity Contract [Member] | Maximum [Member] | Atlantic City Electric Co [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