Materials Technologies Separation (Narrative) (Details) $ in Millions		3 Months Ended		9 Months Ended
	Oct. 01, 2016	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Income (loss) from discontinued operations, net of tax		$ 43.2	$ (2.3)	$ 42.2	$ 1,871.5
Business separation costs, legal and advisory fees, before tax		0.0	0.0	0.0	32.5
Materials Technologies
Restructuring Cost and Reserve [Line Items]
Net business separation costs					30.2
Tax benefit related to changes in tax positions on business separation activities			8.2		5.5
Materials Technologies | Business separation costs
Restructuring Cost and Reserve [Line Items]
Business separation costs, legal and advisory fees, before tax					32.5
Materials Technologies | Other non-operating income (expense), net
Restructuring Cost and Reserve [Line Items]
Pension settlement benefit					2.3
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff | Electronic Materials Division (EMD)
Restructuring Cost and Reserve [Line Items]
Distribution ratio of common stock in spin-off	0.5
Discontinued Operations | Electronic Materials Division (EMD)
Restructuring Cost and Reserve [Line Items]
Income (loss) from discontinued operations, net of tax		0.0	$ 0.0	0.0	$ 0.0
Assets of discontinued operations		0.0		0.0		$ 0.0
Liabilities of discontinued operations		$ 0.0		$ 0.0		$ 0.0