Fair Value Disclosures (Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 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	2	5
Included in accumulated other comprehensive loss
Purchases
Issuances		(1)
Settlements		(4)
Ending Balance	19	19
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	2	5
Included in accumulated other comprehensive loss
Purchases
Issuances		(1)
Settlements		(4)
Ending Balance	19	18
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
Purchases
Ending Balance	1	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	(3)	(2)
Purchases
Settlements	9	8
Transfers in (out) of level 3		(4)
Ending Balance	(11)	(21)
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	(3)	(2)
Purchases
Settlements	8	8
Ending Balance	(10)	(17)
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 regulatory assets	(1)
Purchases
Ending Balance	$ (1)