Share-based Payments (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Stock options, Weighted Average Exercise Price
Vesting period	3 years
Recognized compensation expense	$ 26.5	$ 31.8
Unrecognized compensation expense	$ 59.8		$ 74.6
Employee Stock Option
Shares of stock under options
Balance at the beginning of the period (in shares)	0.1	0.6
Options forfeited or expired ( in shares)		(0.5)
Balance at the end of the period (in shares)	0.1	0.1
Vested and expected to vest in the future at the end of the period (in shares)	0.1	0.1
Stock options, Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 31.62	$ 31.62
Options forfeited or expired (in dollars per share)		31.62
Balance at the end of the period (in dollars per share)	31.62	31.62
Vested and expected to vest in the future at the end of the period (in dollars per share)	$ 31.62	31.62
Performance Earnings Program
Stock options, Weighted Average Exercise Price
Vesting period	3 years
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 43.02	27.51
Restricted Stock Units (RSUs)
Stock options, Weighted Average Exercise Price
Weighted average grant-date fair value of stock options granted (in dollars per share)	$ 42.27	$ 27.67

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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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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Number of options outstanding, including both vested and non-vested options.

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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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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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