Summary Of Significant Accounting Policies (Schedule Of Amortization Expense For Intangible Assets) (Details) (USD $) In Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Summary Of Significant Accounting Policies [Abstract]
Amortization expense based on usage of emission allowances	$ 1	$ 10	[1]	$ 2	[1]	$ 20	[1]

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