Income Taxes (Details) (USD $) In Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Current tax expense (benefit):
Federal									$ (53.6)	$ (153.1)	$ (213.9)
State									(6.1)	7.5	(6.6)
Total current tax expense (benefit)									(59.7)	(145.6)	(220.5)
Deferred tax expense:
Federal									0		200.7
State									0		12.8
Total deferred tax expense (benefit)									0		213.5
Total income tax benefit	$ (1.9)	$ 0.2	$ (58.6)	$ 0.5	$ 7.2	$ (4.2)	$ 0.7	$ (149.2)	$ (59.7)	$ (145.6)	$ (7.0)