Business Segment Information - Narrative (Details) $ in Millions	12 Months Ended
Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments \| segment	2
Identifiable assets	$ 6,262.0	$ 7,161.7	$ 7,101.2
Capital expenditures	125.5	141.7	116.9
Corporate
Segment Reporting Information [Line Items]
Identifiable assets	2,378.2	2,600.7	3,012.3
Capital expenditures	57.6	69.6	50.7
Corporate \| Shared by segments and used in operating activities
Segment Reporting Information [Line Items]
Identifiable assets	234.4	259.3	264.8
Capital expenditures	$ 57.6	$ 69.6	$ 50.7
Sales Revenue, Net \| Customer Concentration Risk
Segment Reporting Information [Line Items]
Portion of total sales to largest distributor	10.00%	10.00%	10.00%

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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