Income Taxes (Details) (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
Current tax expense (benefit):
Federal									$ 66.6	$ (7.0)	$ (53.6)
State									6.8	3.1	(6.1)
Total current tax expense (benefit)									73.4	(3.9)	(59.7)
Deferred tax expense:
Federal									146.3	(616.1)	0
State									(24.6)	(93.4)	0
Total deferred tax expense (benefit)									121.7	(709.5)	0
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)
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation									6.7
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax									$ (1.1)