Income Taxes (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent									29.70%
Federal statutory rate									35.00%
Comparison of income tax expense (benefit) and tax computed at the statutory rate
Income taxes at federal statutory rate									$ 230.2	$ 85.0	$ 4.2
Increase (decrease) in tax resulting from:
State income taxes, net of federal benefit									6.5	12.1	2.4
Domestic production activities deduction									(6.5)	0	0
Uncertain tax positions, net of deferred tax									(12.7)	(2.3)	(11.2)
Valuation allowance									(24.1)	(806.6)	(54.1)
Tax credits									(1.1)	(1.3)	(2.2)
Other									2.8	(0.3)	1.2
Total income tax expense (benefit)	$ 63.3	$ 59.1	$ 31.1	$ 41.6	$ (0.9)	$ (715.6)	$ 1.7	$ 1.5	$ 195.1	$ (713.4)	$ (59.7)