Retirement Plans - Summary of Components of Net Pension Cost and Summary of Components of Postretirement Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6.6	$ 7.5
Interest cost	65.5	63.7
Expected return on plan assets	$ (76.0)	$ (75.8)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component
Amortization of net actuarial loss (gain)	$ 8.1	$ 14.5
Amortization of prior service cost (credit)	$ 1.7	$ 2.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component
Company defined benefit plan cost	$ 5.9	$ 12.0
Multiemployer and other plans	0.4	0.3
Net pension cost	6.3	12.3
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.2
Interest cost	1.9	1.8
Amortization of net actuarial loss (gain)	(1.3)	(1.1)
Amortization of prior service cost (credit)	$ (0.1)	$ (0.2)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component
Net pension cost	$ 0.7	$ 0.7