Retirement Benefits (Schedule of Net Periodic Benefit Cost) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlements	$ 5.0
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	5.3	$ 6.4	$ 10.7	$ 12.8
Interest cost	28.4	26.8	56.8	53.5
Expected return on plan assets	(43.1)	(50.4)	(86.2)	(100.8)
Prior service cost amortization	0.3	0.4	0.6	0.8
Actuarial loss amortization	16.5	22.2	32.6	43.9
Settlements	5.0	1.5	5.8	3.3
Special termination benefits	0.0	0.4	0.7	0.4
Other	0.0	0.0	0.0	0.0
Net periodic benefit cost	12.4	7.3	21.0	13.9
International
Defined Benefit Plan Disclosure [Line Items]
Service cost	4.9	6.6	9.8	12.9
Interest cost	9.0	9.6	18.0	18.8
Expected return on plan assets	(19.2)	(21.1)	(38.1)	(41.3)
Prior service cost amortization	0.1	0.0	0.1	0.0
Actuarial loss amortization	2.8	10.3	5.6	20.3
Settlements	0.0	0.0	0.2	0.0
Special termination benefits	0.0	0.0	0.0	0.0
Other	0.1	0.1	0.4	0.6
Net periodic benefit cost	$ (2.3)	$ 5.5	$ (4.0)	$ 11.3