Derivative Instruments And Hedging Activities (Schedule Of Cash Collateral Offset Against Derivative Positions) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Derivative [Line Items]
Cash collateral pledged to counterparties with the right to reclaim	$ 18	[1]	$ 73	[1]
Delmarva Power & Light Co/De [Member]
Derivative [Line Items]
Cash collateral pledged to counterparties with the right to reclaim			$ 2

[1] Includes cash deposits on commodity brokerage accounts.