Business Separation, Restructuring, and Cost Reduction Actions (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	$ 4.2	$ 0.6	$ 4.1
Restructuring charge	2.0	4.7	(0.7)
Cash receipts (payments)	(3.0)	(1.1)	(1.8)
Non-cash expenses	0.0	0.0	(1.0)
Restructuring reserve, ending balance	3.2	4.2	0.6
Severance and Other Benefits
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	4.2	0.6	4.1
Restructuring charge	2.0	4.7	2.5
Cash receipts (payments)	(3.0)	(1.1)	(6.0)
Non-cash expenses	0.0	0.0	0.0
Restructuring reserve, ending balance	3.2	4.2	0.6
Asset Actions/Other
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning balance	0.0	0.0	0.0
Restructuring charge	0.0	0.0	(3.2)
Cash receipts (payments)	0.0	0.0	4.2
Non-cash expenses	0.0	0.0	(1.0)
Restructuring reserve, ending balance	$ 0.0	$ 0.0	$ 0.0