Employee Benefit Plans - Deferred Compensation Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined Contribution Plan, Cost	$ 40.2	$ 35.4	$ 30.3
Supplemental Executive Retirement Plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	58.9	52.1
Compensation expense (reduction in expense)	8.3	7.7	7.0
Deferred Compensation Plan For Select Group Of Employees [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	148.2	119.5
Compensation expense (reduction in expense)	$ 17.0	$ (24.0)	$ 21.7