Retirement Benefits (Components Recognized in Accumulated Other Comprehensive Income on Pretax Basis) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
U.S.
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 980.5	$ 1,273.6
Prior service cost (credit)	8.1	8.5
Net transition liability	0.0	0.0
Total	988.6	1,282.1
International
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	551.9	769.6
Prior service cost (credit)	(1.8)	(1.9)
Net transition liability	0.4	0.4
Total	$ 550.5	$ 768.1