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Share-Based Payments - Exercisable Options (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Compensation expense
Allocated Share-based Compensation Expense	$ 73.1	$ 83.8	$ 73.4
Unrecognized compensation expense	$ 94.3	96.8
Vesting period	3 years
Employee Stock Option
Stock Incentive Plans, additional disclosures
Aggregate intrinsic value of stock options exercised	$ 0.9	$ 1.2	$ 0.6
Compensation expense
Number of stock options granted during the period	0	0
Performance Earnings Program
Compensation expense
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 37.69	$ 38.15	$ 29.91
Performance period over which objectives must be met to qualify for an award grant	3 years
Restricted Stock Units (RSUs)
Compensation expense
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 36.83	$ 37.96	$ 29.82
$31.62 | Employee Stock Option
Options Outstanding
Number outstanding as of end of period (in shares)	600,000
Weighted Average Remaining Contractual Life	5 years 5 months 5 days
Weighted Average Exercise Price (in dollars per share)	$ 31.62
Aggregate Intrinsic Value (in millions)	$ 0.7

X

- Definition

The period of time over which the employee needs to meet the performance objectives in order to qualify for the stock unit award in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to all outstanding stock options which are in the customized range of exercise prices as of the balance sheet date.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
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Unrecognized cost of unvested share-based compensation awards.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

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Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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