v3.25.2
Employee Benefit Plans - Components of Pension and Other Postretirement Benefit Income (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Pension benefits        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost $ 17.4 $ 20.7 $ 52.3 $ 62.5
Expected return on plan assets (18.1) (17.2) (54.2) (51.5)
Amortization of prior service costs (credits) 0.1 0.1 0.1 0.1
Net periodic benefit (income) costs (0.6) 3.6 (1.8) 11.1
Other postretirement benefits        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 0.3 0.3 0.8 0.9
Expected return on plan assets 0.0 0.0 0.0 0.0
Amortization of prior service costs (credits) (0.6) (0.5) (1.7) (1.6)
Net periodic benefit (income) costs $ (0.3) $ (0.2) $ (0.9) $ (0.7)