Employee Benefit Plans - Schedule of Changes in The Benefit Obligations and Plan Assets, The Funded Status of The Plans and The Amounts Recognized in The Balance Sheet (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 594.2	$ 601.1
Change in projected benefit obligation
Benefit obligation at the beginning of the period	613.6	546.5
Service cost	11.5	10.1	$ 9.1
Interest cost	16.4	17.1	18.7
Actuarial loss (gain)	(22.6)	44.0
Plan amendments		9.8
Benefits paid	(16.4)	(15.8)
Currency translation adjustments	1.7	1.9
Benefit obligation at the end of the period	604.2	613.6	546.5
Change in plan assets
Fair value of plan assets at the beginning of the period	437.3	408.9
Actual return on plan assets	71.3	35.4
Company contributions	25.2	11.4
Expenses paid	(2.9)	(4.3)
Benefits paid	(16.4)	(15.8)
Currency translation adjustments	1.4	1.7
Fair value of plan assets at the end of the period	515.9	437.3	408.9
Funded status of plan - underfunded at September 30	(88.3)	(176.3)
Recognized in consolidated balance sheet at September 30
Prepaid benefit cost (long-term asset)	2.1
Accrued benefit liability (current liability)	(2.0)	(1.9)
Accrued benefit liability (long-term liability)	(88.4)	(174.4)
Total	(88.3)	(176.3)
Postretirement Health and Other
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	53.3	53.3
Change in projected benefit obligation
Benefit obligation at the beginning of the period	53.3	51.4
Service cost	2.2	3.5	3.1
Interest cost	1.2	1.6	1.9
Actuarial loss (gain)	(1.1)	5.4
Plan amendments		(6.5)
Benefits paid	(2.3)	(2.1)
Benefit obligation at the end of the period	53.3	53.3	$ 51.4
Change in plan assets
Company contributions	2.3	2.1
Benefits paid	(2.3)	(2.1)
Funded status of plan - underfunded at September 30	(53.3)	(53.3)
Recognized in consolidated balance sheet at September 30
Accrued benefit liability (current liability)	(2.4)	(2.5)
Accrued benefit liability (long-term liability)	(50.9)	(50.8)
Total	$ (53.3)	$ (53.3)

Employee Benefit Plans - Schedule of Changes in The Benefit Obligations and Plan Assets, The Funded Status of The Plans and The Amounts Recognized in The Balance Sheet (Details) - USD ($)
$ in Millions

12 Months Ended

Sep. 30, 2021

Sep. 30, 2020

Sep. 30, 2019

Pension Plan

Defined Benefit Plan Disclosure [Line Items]

Accumulated benefit obligation

$ 594.2

$ 601.1

Change in projected benefit obligation

Benefit obligation at the beginning of the period

613.6