Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Sep. 30, 2024
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]			Other non-operating income (expense), net	Other non-operating income (expense), net
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Company contributions			$ 14.3	$ 19.2	$ 34.7
Defined Benefit Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	$ 30.0		30.0
Defined Benefit Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	40.0		40.0
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Amortization of actuarial gain	$ 0.1	$ 0.2	$ 0.4	$ 0.3