Retirement Benefits (Amounts Recognized on Balance Sheet) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	$ 18.4	$ 0.0
Accrued liabilities	(22.6)	(35.5)
Defined Benefit Pension Plan | U.S.
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	5.3	0.0
Accrued liabilities	(12.6)	(24.1)
Noncurrent liabilities	(481.2)	(748.3)
Net Amount Recognized	(488.5)	(772.4)
Defined Benefit Pension Plan | International
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	13.1	0.0
Accrued liabilities	0.0	0.0
Noncurrent liabilities	(222.6)	(438.5)
Net Amount Recognized	$ (209.5)	$ (438.5)