Income Taxes - Provisions for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Current expense (benefit):
Federal	$ 97.1	$ 102.4	$ 53.3
State	32.2	30.7	25.1
Foreign	36.0	37.0	37.3
Investment tax credit	(1.2)	(1.6)	(1.6)
Total current expense	164.1	168.5	114.1
Deferred expense (benefit):
Federal	28.1	61.9	54.6
State	2.9	7.8	(0.7)
Foreign	(17.0)	(2.7)	(4.9)
Investment tax credit amortization	(0.3)	(0.3)	(0.3)
Total deferred expense	13.7	66.7	48.7
Total income tax expense	$ 177.8	$ 235.2	$ 162.8