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, 2013	Sep. 30, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in income	$ 3	$ 3
Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(4)	(15)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets		(2)
Purchases
Issuances
Settlements	4	10
Transfers in (out) of level 3
Ending balance		(7)
Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	18	17
Included in income	3	3
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets
Purchases
Issuances	(3)	(3)
Settlements
Transfers in (out) of level 3
Ending balance	18	17
Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(3)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets	(7)	(1)
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Ending balance	(10)	(1)
Potomac Electric Power Co [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Included in income	3	3
Potomac Electric Power Co [Member] | Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	18	17
Included in income	3	3
Included in accumulated other comprehensive loss
Purchases
Issuances	(3)	(3)
Settlements	(1)
Transfers in (out) of level 3
Ending balance	17	17
Delmarva Power & Light Co/De [Member] | Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(4)	(15)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets		(2)
Purchases
Issuances
Settlements	4	10
Transfers in (out) of level 3
Ending balance		(7)
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 income
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Ending balance	1	1
Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(3)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities and regulatory assets	(7)	(1)
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Ending balance	$ (10)	$ (1)