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Employee Benefit Plans - Schedule of Fair Values of Plan Assets by Investment Category (Details) - Pension benefits - USD ($)
$ in Millions
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 1,365.5 $ 1,452.9 $ 1,361.0
Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 24.9 25.4  
Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,139.2 1,210.3  
Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 201.4 217.2  
Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 24.9 25.4  
Cash and cash equivalents | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 24.9 25.4  
Cash and cash equivalents | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Cash and cash equivalents | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Cash and cash equivalents | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
U.S. government securities and futures      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 85.0 49.6  
U.S. government securities and futures | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
U.S. government securities and futures | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 85.0 49.6  
U.S. government securities and futures | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
U.S. government securities and futures | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other government securities      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 41.3 42.1  
Other government securities | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other government securities | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 41.3 42.1  
Other government securities | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other government securities | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Corporate debt instruments      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,002.3 1,108.4  
Corporate debt instruments | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Corporate debt instruments | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,002.3 1,108.4  
Corporate debt instruments | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Corporate debt instruments | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Private equity and hedge funds      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.6 1.2  
Private equity and hedge funds | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Private equity and hedge funds | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Private equity and hedge funds | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Private equity and hedge funds | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.6 1.2  
Collective trust funds      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 200.8 216.0  
Collective trust funds | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Collective trust funds | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Collective trust funds | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Collective trust funds | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 200.8 216.0  
Other investments      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 10.6 10.2  
Other investments | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other investments | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 10.6 10.2  
Other investments | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other investments | Assets measured at NAV      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 0.0 $ 0.0