Income Taxes - Provisions for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Current expense (benefit):
Federal	$ 102.4	$ 53.3	$ (10.4)
State	30.7	25.1	11.2
Foreign	37.0	37.3	18.8
Investment tax credit	(1.6)	(1.6)	(2.9)
Total current expense	168.5	114.1	16.7
Deferred expense (benefit):
Federal	61.9	54.6	81.7
State	7.8	(0.7)	7.0
Foreign	(2.7)	(4.9)	1.8
Investment tax credit amortization	(0.3)	(0.3)	(0.3)
Total deferred expense	66.7	48.7	90.2
Total income tax expense	$ 235.2	$ 162.8	$ 106.9