Fair Value Disclosures (Reconciliations Of Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (4)	$ (15)
Included in accumulated other comprehensive loss
Included in regulatory assets (liabilities)		(3)
Purchases
Settlements	4	6
Transfers in (out) of level 3
Ending balance		(12)
Natural Gas [Member] | Delmarva Power & Light Co/De [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(4)	(15)
Included in accumulated other comprehensive loss
Included in regulatory assets (liabilities)		(3)
Purchases
Settlements	4	6
Transfers in (out) of level 3
Ending balance		(12)
Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	18	17
Included in income	1	1
Included in accumulated other comprehensive loss
Purchases
Transfers in (out) of level 3
Ending balance	19	18
Life Insurance Contracts [Member] | Potomac Electric Power Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	18	17
Included in income	1	1
Included in accumulated other comprehensive loss
Purchases
Issuances	(1)
Transfers in (out) of level 3
Ending balance	18	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
Transfers in (out) of level 3
Ending balance	1	1
Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(3)
Included in accumulated other comprehensive loss
Purchases
Transfers in (out) of level 3
Ending balance	(3)
Capacity [Member] | Atlantic City Electric Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(3)
Included in accumulated other comprehensive loss
Purchases
Transfers in (out) of level 3
Ending balance	$ (3)