Retirement Benefits - Schedule of Amounts Included in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	$ (61.3)	$ (30.7)
Net actuarial loss	503.9	718.7
Total	442.6	688.0
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost	4.7	4.1
Net actuarial loss	0.5	2.0
Total	$ 5.2	$ 6.1