Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Gain) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
North America | Pension Benefits
Components of net periodic benefit cost (gain)
Service cost	$ 0.9	$ 1.1	$ 2.8	$ 3.2
Interest cost	1.1	0.9	3.1	2.7
Expected return on plan assets	(1.6)	(1.1)	(4.8)	(3.3)
Recognized net actuarial loss	0.0	0.3	0.0	0.9
Recognized prior service cost (credit)	0.0	0.0	0.1	0.0
Net periodic benefit cost (gain)	0.4	1.2	1.2	3.5
North America | Other Postretirement Benefit Plan
Components of net periodic benefit cost (gain)
Service cost	0.2	0.1	0.4	0.4
Interest cost	0.5	0.6	1.6	1.6
Recognized net actuarial loss	0.0	0.1	0.0	0.2
Recognized prior service cost (credit)	(1.2)	(1.2)	(3.6)	(3.5)
Net periodic benefit cost (gain)	(0.5)	(0.4)	(1.6)	(1.3)
International Pension Plans | Non-North America | Pension Benefits
Components of net periodic benefit cost (gain)
Service cost	1.4	1.7	4.3	5.1
Interest cost	4.7	5.0	14.3	14.9
Expected return on plan assets	(7.2)	(8.1)	(21.8)	(24.1)
Net periodic benefit cost (gain)	$ (1.1)	$ (1.4)	$ (3.2)	$ (4.1)