Condensed Consolidated Statement of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Common shares	Treasury shares	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)			(11,200,000)
Common shares, issued (in shares)		65,200,000
Total shareholders' equity at Sep. 30, 2018	$ 1,744.6	$ 0.7	$ (819.2)	$ 1,628.3	$ 1,083.1	$ (148.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	(0.4)				(0.4)
Foreign currency translation adjustments	(10.8)					(10.8)
Pension and postretirement activity, net of tax	0.0					0.0
Deferred (loss) gain on hedging activity, net of tax	(1.3)					(1.3)
Impact of ASU 2016-16	3.9				3.9
Activity under share plans (in shares)			100,000
Activity under share plans (in usd)	3.3		$ 6.6	3.3	0.0
Total shareholders' equity at Dec. 31, 2018	$ 1,739.3	$ 0.7	$ (812.6)	1,625.0	1,086.6	(160.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)			(11,100,000)
Common shares, issued (in shares)		65,200,000
Treasury shares (in shares)	11,045,243		(11,000,000.0)
Common shares, issued (in shares)	65,251,989	65,200,000
Total shareholders' equity at Sep. 30, 2019	$ 1,303.5	$ 0.7	$ (803.8)	1,627.7	714.8	(235.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	22.4				22.4
Foreign currency translation adjustments	21.5					21.5
Pension and postretirement activity, net of tax	(1.5)					(1.5)
Deferred (loss) gain on hedging activity, net of tax	(1.3)					(1.3)
Activity under share plans (in shares)			100,000
Activity under share plans (in usd)	3.5		$ 8.5	5.0	0.0
Total shareholders' equity at Dec. 31, 2019	$ 1,348.1	$ 0.7	$ (795.3)	$ 1,622.7	$ 737.2	$ (217.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares (in shares)	10,951,905		(10,900,000)
Common shares, issued (in shares)	65,251,989	65,200,000