Derivative Instruments - Schedule of Fair Value of Derivatives (Details) - Level 2 - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Assets and liabilities measured at fair value on a recurring basis
Net derivative asset / (liability) designated as hedging instruments	$ (12.1)	$ (16.1)
Net derivative asset / (liability) not designated as hedging instruments	2.9	(11.4)
Forward exchange contracts \| Other current assets
Assets and liabilities measured at fair value on a recurring basis
Forward exchange contracts designated as hedging instruments	15.8	12.4
Forward exchange contracts not designated as hedging instruments	3.4	0.8
Forward exchange contracts \| Other assets
Assets and liabilities measured at fair value on a recurring basis
Forward exchange contracts designated as hedging instruments	1.9	0.3
Forward exchange contracts not designated as hedging instruments	0.6	0.0
Forward exchange contracts \| Other current liabilities
Assets and liabilities measured at fair value on a recurring basis
Forward exchange contracts designated as hedging instruments	(5.1)	(19.1)
Forward exchange contracts not designated as hedging instruments	(1.1)	(12.2)
Forward exchange contracts \| Other liabilities
Assets and liabilities measured at fair value on a recurring basis
Forward exchange contracts designated as hedging instruments	(0.7)	(5.1)
Interest rate swap contracts \| Other liabilities
Assets and liabilities measured at fair value on a recurring basis
Interest rate swap contracts designated as hedging instruments	$ (24.0)	$ (4.6)

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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Fair value as of the balance sheet date of all foreign currency derivative assets designated as cash flow hedging instruments.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
-Section 50
-Paragraph 4B
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