Fair Value Disclosures (Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 17	$ 19
Included in income	3	5
Included in accumulated other comprehensive loss
Purchases
Issuances	(3)	(3)
Settlements		(4)
Ending Balance	17	17
Life Insurance Contracts [Member] | Potomac Electric Power Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	17	18
Included in income	3	5
Included in accumulated other comprehensive loss
Purchases
Issuances	(3)	(3)
Settlements		(4)
Ending Balance	17	16
Life Insurance Contracts [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1	1
Included in accumulated other comprehensive loss
Included in regulatory assets
Purchases
Ending Balance	1	1
Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in accumulated other comprehensive loss
Included in regulatory assets	(1)
Purchases
Ending Balance	(1)
Capacity [Member] | Atlantic City Electric Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in accumulated other comprehensive loss
Included in regulatory assets	(1)
Purchases
Ending Balance	(1)
Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(17)	(23)
Included in accumulated other comprehensive loss
Included in regulatory assets	(2)	(6)
Purchases
Settlements	11	11
Transfers in (out) of level 3		1
Ending Balance	(8)	(17)
Natural Gas [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(15)	(23)
Included in accumulated other comprehensive loss
Included in regulatory assets	(2)	(6)
Purchases
Settlements	10	11
Ending Balance	$ (7)	$ (18)