Summary Of Significant Accounting Policies (Schedule Of Amortization Expense) (Details) (Emission Allowances [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Emission Allowances [Member]
Amortization expense	$ 6	[1]	$ 35	[1]	$ 40	[1]

[1] Includes allowances consumed that were recorded through purchase accounting.