Retirement Benefits (Schedule of Net Periodic Benefit Cost) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5.3	$ 5.8	$ 10.7	$ 11.6
Interest cost	17.3	22.8	34.5	45.6
Expected return on plan assets	(48.7)	(47.2)	(97.3)	(94.4)
Prior service cost amortization	0.3	0.3	0.6	0.6
Actuarial loss amortization	19.6	21.0	39.3	42.0
Settlements	0.0	1.5	0.0	1.5
Other	0.0	0.0	0.0	0.0
Net periodic benefit cost	(6.2)	4.2	(12.2)	6.9
International
Defined Benefit Plan Disclosure [Line Items]
Service cost	5.9	5.8	11.6	11.7
Interest cost	6.3	6.2	12.4	12.4
Expected return on plan assets	(21.0)	(19.4)	(41.2)	(38.9)
Prior service cost amortization	0.0	0.0	0.0	0.0
Actuarial loss amortization	4.8	4.9	9.4	9.8
Settlements	0.0	0.0	0.0	0.0
Other	0.2	0.2	0.5	0.4
Net periodic benefit cost	$ (3.8)	$ (2.3)	$ (7.3)	$ (4.6)