Basis of Presentation and Accounting Policies - Narrative (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Accounting Policies [Abstract]
Allowance for doubtful accounts	$ 24.1		$ 24.9
Allowance for certain customer returns, rebates and incentives	$ 16.5		$ 11.9
Common shares excluded from computation of earnings per share amount	2.8
Antidilutive share-based compensation awards	1.9	1.0
Capital expenditures in accounts payable or other current liabilities at period end	$ 13.0	$ 12.9
Outstanding purchase of common stock recorded in accounts payable	$ 17.8	$ 4.5