Employee Benefit Plans - Components of Pension and Other Postretirement Benefit Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 20.6	$ 10.8
Expected return on plan assets	(16.8)	(19.7)
Amortization of prior service credits	0.0	0.0
Net periodic benefit costs (income)	3.8	(8.9)
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0.4	0.2
Expected return on plan assets	0.0	0.0
Amortization of prior service credits	(0.5)	(0.6)
Net periodic benefit costs (income)	$ (0.1)	$ (0.4)