Basis of Presentation and Accounting Policies - Narrative (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017
Accounting Policies [Abstract]
Allowance for doubtful accounts	$ 19.7		$ 19.7		$ 24.9
Allowance for certain customer returns, rebates and incentives	$ 7.8		$ 7.8		$ 11.9
Antidilutive share-based compensation awards (in shares)	0.9	0.6	0.9	0.8
Capital expenditures in accounts payable or other current liabilities at period end			$ 13.4	$ 22.3
Outstanding purchase of common stock recorded in accounts payable			$ 22.6	$ 3.4