Retirement Benefits (Components Recognized in Accumulated Other Comprehensive Income on Pretax Basis) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
U.S.
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 444.7	$ 797.7
Prior service cost	6.3	7.0
Net transition liability	0.0	0.0
Total	451.0	804.7
International
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	535.8	643.2
Prior service cost	3.6	3.6
Net transition liability	0.4	0.4
Total	$ 539.8	$ 647.2