Pension Plans - Schedule of Net Benefit Costs (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.0	$ 0.0
Interest cost	4.0	5.1
Expected return on plan assets	(6.1)	(6.5)
Amortization of unrecognized net losses	1.6	1.0
Net periodic (benefit)/cost	(0.5)	(0.4)
International
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.1
Interest cost	0.3	0.7
Expected return on plan assets	(0.6)	(1.2)
Amortization of unrecognized net losses	0.3	0.3
Net periodic (benefit)/cost	$ 0.2	$ (0.1)