Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Company contributions			$ 16.1	$ 27.7	$ 44.6
Defined Benefit Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	$ 40.0		40.0
Defined Benefit Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for current fiscal year	50.0		50.0
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Amortization of actuarial gain	$ 0.4	$ 0.5	$ 0.8	$ 0.9