Derivative Instruments And Hedging Activities (Schedule Of Cash Collateral Offset Against Derivative Positions) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Derivative Instruments And Hedging Activities [Abstract]
Cash collateral pledged to counterparties with the right to reclaim	$ 73	[1]	$ 122	[1]

[1] Includes cash deposits on commodity brokerage accounts.