Cost Reduction and Asset Actions (Carrying Amount of Accrual) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Cost reduction and asset actions	$ 0.0	$ 10.3	$ 0.0	$ 60.3	$ 151.4
Cost Reduction Actions
Restructuring Cost and Reserve [Line Items]
Cost reduction and asset actions					154.8
Noncash expenses					(84.2)
Amount reflected in pension liability			(0.4)		(2.0)
Amount reflected in other noncurrent liabilities					(2.2)
Cash expenditures			(24.1)		(36.9)
Currency translation adjustment			0.7		(0.3)
Accrued balance	17.7		17.7		41.5	$ 12.3
Cost Reduction Actions | Severance And Other Benefits
Restructuring Cost and Reserve [Line Items]
Cost reduction and asset actions		$ 10.3		18.0	66.3
Noncash expenses					0.0
Amount reflected in pension liability			(0.4)		(2.0)
Amount reflected in other noncurrent liabilities					0.0
Cash expenditures			(23.9)		(35.7)
Currency translation adjustment			0.7		(0.3)
Accrued balance	17.0		17.0		40.6	12.3
Cost Reduction Actions | Asset Actions/Other
Restructuring Cost and Reserve [Line Items]
Cost reduction and asset actions				$ 45.7	88.5
Noncash expenses					(84.2)
Amount reflected in pension liability			0.0		0.0
Amount reflected in other noncurrent liabilities					(2.2)
Cash expenditures			(0.2)		(1.2)
Currency translation adjustment			0.0		0.0
Accrued balance	$ 0.7		$ 0.7		$ 0.9	$ 0.0