Pension Plans (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized on other pension plans	$ 0.0	$ 3.7	$ 14.1
United States | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0
Interest cost	15.9	20.4	18.7
Expected return on plan assets	(24.3)	(26.2)	(30.1)
Recognized net actuarial loss	6.5	4.1	4.4
Settlement loss recognized on other pension plans	0.0	0.0	0.1
Net periodic (benefit)/expense	(1.9)	(1.7)	(6.9)
United States | Canadian Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized on other pension plans	0.0	0.0	0.0
United States | Ireland Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized on other pension plans	0.0	0.0	0.0
International | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.8	0.5	0.6
Interest cost	1.5	2.9	3.9
Expected return on plan assets	(3.6)	(4.9)	(6.3)
Recognized net actuarial loss	1.5	0.9	2.0
Settlement loss recognized on other pension plans	0.5	0.4	1.0
Net periodic (benefit)/expense	0.7	3.5	15.3
International | Canadian Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized on other pension plans	0.0	0.0	14.1
International | Ireland Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized on other pension plans	$ 0.0	$ 3.7	$ 0.0