Fair Value Disclosures (Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 17	$ 19
Included in income	4	6
Included in accumulated other comprehensive loss
Purchases
Issuances	(3)	(3)
Settlements		(5)
Ending Balance	18	17
Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets	(3)
Purchases
Ending Balance	(3)
Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	(17)	(23)
Included in income	2	(4)
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets	(2)	(10)
Purchases
Settlements	13	19
Transfers in (out) of level 3		1
Ending Balance	(4)	(17)
Potomac Electric Power Co [Member] | Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	17	18
Included in income	4	6
Included in accumulated other comprehensive loss
Purchases
Issuances	(3)	(3)
Settlements		(4)
Ending Balance	18	17
Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets	(3)
Purchases
Ending Balance	(3)
Delmarva Power & Light Co/De [Member] | Life Insurance Contracts [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
Delmarva Power & Light Co/De [Member] | Natural Gas [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 liabilities and regulatory assets	(2)	(10)
Purchases
Settlements	13	18
Ending Balance	$ (4)	$ (15)