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, 2014	Mar. 31, 2013
Life Insurance Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 19	$ 18
Included in income	1	1
Included in accumulated other comprehensive loss
Included in regulatory liabilities
Purchases
Issuances	(1)
Settlements
Transfers in (out) of level 3
Ending balance	19	19
Natural Gas [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		(4)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities
Purchases
Issuances
Settlements		4
Transfers in (out) of level 3
Ending balance
Capacity Segment [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
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Ending balance		(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	18
Included in income	1	1
Included in accumulated other comprehensive loss
Purchases
Issuances	(1)	(1)
Settlements
Transfers in (out) of level 3
Ending balance	18	18
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
Purchases
Issuances
Settlements
Transfers in (out) of level 3
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		(4)
Included in income
Included in accumulated other comprehensive loss
Included in regulatory liabilities
Purchases
Issuances
Settlements		4
Transfers in (out) of level 3
Ending balance
Atlantic City Electric Co [Member] | Capacity Segment [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
Purchases
Issuances
Settlements
Transfers in (out) of level 3
Ending balance		$ (3)