Income Taxes (Narrative) (Details) (USD $)	12 Months Ended				1 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Illinois Corporate Income Tax [Member]	Jan. 31, 2011 Minimum [Member] Illinois Corporate Income Tax [Member]	Jan. 31, 2011 Maximum [Member] Illinois Corporate Income Tax [Member]	Dec. 31, 2025 Scenario, Plan [Member] Minimum [Member] Illinois Corporate Income Tax [Member]	Dec. 31, 2015 Scenario, Plan [Member] Maximum [Member] Illinois Corporate Income Tax [Member]
State corporate income tax rate	4.00%	8.00%	5.00%		7.30%	9.50%	7.30%	7.75%
Increase in current state and local tax expense benefit				$ 6,000,000
Decrease in deferred state and local income tax expense benefit				2,000,000
Reduction of uncertain tax positions	$ 39,000,000