Pension Plans - Schedule of Net Benefit Costs (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Interest cost	4.0	5.1	12.0	15.3
Expected return on plan assets	(6.1)	(6.6)	(18.3)	(19.6)
Amortization of unrecognized net losses	1.6	1.1	4.8	3.1
Net periodic (benefit)/cost	(0.5)	(0.4)	(1.5)	(1.2)
International
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.1	0.6	0.4
Interest cost	0.3	0.8	0.9	2.3
Expected return on plan assets	(0.6)	(1.3)	(1.8)	(3.8)
Amortization of unrecognized net losses	0.3	0.2	0.9	0.7
Net periodic (benefit)/cost	$ 0.2	$ (0.2)	$ 0.6	$ (0.4)