Retirement Benefits - Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Retirement Benefits [Abstract]
Non-current liabilities	$ (20.0)	$ (16.0)
Accumulated other comprehensive loss, net of taxes	$ (3.4)	$ (2.2)	$ 0.0

Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 50
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Name:	us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant