Business Separation, Restructuring, and Cost Reduction Actions (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 0.6	$ 4.1	$ 0.9
Restructuring charge	4.7	(0.7)	21.6
Cash receipts (payments)	(1.1)	(1.8)	(11.2)
Non-cash expenses	0.0	(1.0)	(7.2)
Restructuring reserve, ending balance	4.2	0.6	4.1
Severance and Other Benefits
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0.6	4.1	0.9
Restructuring charge	4.7	2.5	14.4
Cash receipts (payments)	(1.1)	(6.0)	(11.2)
Non-cash expenses	0.0	0.0	0.0
Restructuring reserve, ending balance	4.2	0.6	4.1
Asset Actions/Other
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0.0	0.0	0.0
Restructuring charge	0.0	(3.2)	7.2
Cash receipts (payments)	0.0	4.2	0.0
Non-cash expenses	0.0	(1.0)	(7.2)
Restructuring reserve, ending balance	$ 0.0	$ 0.0	$ 0.0