v3.25.1
Retirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2025
Mar. 31, 2024
Pension Benefits        
Components of net periodic benefit cost (income)        
Service cost $ 11.0 $ 9.0 $ 21.0 $ 19.0
Interest cost 34.0 37.0 68.0 73.0
Expected return on plan assets (42.0) (43.0) (83.0) (85.0)
Amortization of net actuarial loss 7.0 0.0 13.0 0.0
Net periodic postretirement benefit cost 10.0 3.0 19.0 7.0
Other Postretirement Benefits        
Components of net periodic benefit cost (income)        
Service cost 0.0 0.0 0.0 0.0
Interest cost 0.0 0.0 0.0 1.0
Amortization of net actuarial loss 1.0 1.0 2.0 1.0
Net periodic postretirement benefit cost $ 1.0 $ 1.0 $ 2.0 $ 2.0