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, 2013	Dec. 31, 2012
Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	$ (4)	$ (15)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities		(2)
Purchases
Issuances
Settlements	4	13
Transfers in (out) of level 3
Balance as of December 31		(4)
Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	18	17
Included in income	4	4
Included in accumulated other comprehensive loss
Included in regulatory liabilities
Purchases
Issuances	(3)	(3)
Settlements
Transfers in (out) of level 3
Balance as of December 31	19	18
Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	(3)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities	3	(3)
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Balance as of December 31		(3)
Potomac Electric Power Co [Member] | Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	18	17
Included in income	4	4
Included in accumulated other comprehensive loss
Purchases
Issuances	(3)	(3)
Settlements	(1)
Transfers in (out) of level 3
Balance as of December 31	18	18
Atlantic City Electric Co [Member] | Capacity [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	(3)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities	3	(3)
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Balance as of December 31		(3)
Delmarva Power & Light Co/De [Member] | Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	(4)	(15)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities		(2)
Purchases
Issuances
Settlements	4	13
Transfers in (out) of level 3
Balance as of December 31		(4)
Delmarva Power & Light Co/De [Member] | Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of January 1	1	1
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Balance as of December 31	$ 1	$ 1