Employee Benefit Plans - Time-Based Restricted Stock Unit Equity Awards (Details) - Restricted Stock Units (RSUs) [Member] $ / shares in Units, $ in Millions	12 Months Ended
Sep. 30, 2018 USD ($) grant_recipient $ / shares shares	Sep. 30, 2017 USD ($) grant_recipient $ / shares shares	Sep. 30, 2016 USD ($) grant_recipient $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value \| $	$ 51.0	$ 25.0	$ 12.0
Number of Restricted Stock Units
Outstanding at beginning of year, shares \| shares	4,365,782	3,478,233	1,978,262
Granted, shares \| shares	1,747,870	1,868,660	2,117,330
Vested, shares \| shares	(1,149,055)	(792,941)	(423,427)
Cancelled, shares \| shares	(166,675)	(188,170)	(193,932)
Outstanding at end of year, shares \| shares	4,797,922	4,365,782	3,478,233
Weighted Average Grant Date Fair Value
Outstanding at beginning of year, weighted average grant date fair value, per share \| $ / shares	$ 26.09	$ 24.12	$ 25.60
Granted, weighted average grant date fair value, per share \| $ / shares	41.82	28.64	23.14
Vested, weighted average grant date fair value, per share \| $ / shares	25.80	24.48	25.57
Cancelled, weighted average grant date fair value, per share \| $ / shares	29.56	25.21	25.05
Outstanding at end of year, weighted average grant date fair value, per share \| $ / shares	$ 31.77	$ 26.09	$ 24.12
Additional information - restricted stock units
Share-based compensation expense \| $	$ 39.3	$ 28.8	$ 18.7
Unrecognized compensation expense \| $	$ 101.1
Weighted average period over which unrecognized compensation cost is expected to be recognized	3 years 6 months
Minimum [Member]
Additional information - restricted stock units
Vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Remaining Award Vesting Period	1 year
Maximum [Member]
Additional information - restricted stock units
Vesting period	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Remaining Award Vesting Period	5 years
Fiscal 2018 Grant [Member]
Additional information - restricted stock units
RSU grant recipients \| grant_recipient	920
Fiscal 2017 Grant [Member]
Additional information - restricted stock units
RSU grant recipients \| grant_recipient		600
Fiscal 2016 Grant [Member]
Additional information - restricted stock units
RSU grant recipients \| grant_recipient			570

The number of recipients of a share-based compensation grant.

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Share-based Compensation Arrangement by Share-based Payment Award, Remaining Award Vesting Period

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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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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No definition available.

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