Debt (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
Mar. 31, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Short-term Debt	$ 75.0	$ 0.0
Two Point Two Percentage Senior Notes [Member]
Debt Instrument [Line Items]
Stated Interest Rate	2.20%
Debt Instrument, Face Amount	$ 500.0	500.0
Two Point Two Percentage Senior Notes [Member]
Debt Instrument [Line Items]
Stated Interest Rate	3.75%
Debt Instrument, Face Amount	$ 500.0	500.0
PointThreeSevenTwoPercentageYenDenominatedSeniorNotes [Member]
Debt Instrument [Line Items]
Stated Interest Rate	0.372%
Debt Instrument, Face Amount	$ 767.4	748.4
Three Point One Percentage Senior Notes [Member]
Debt Instrument [Line Items]
Stated Interest Rate	3.50%
Debt Instrument, Face Amount	$ 600.0	$ 600.0
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt covenant compliance	The indentures under which the above notes were issued require us to maintain compliance with certain covenants, including limits on future liens and sale and leaseback transactions on certain material properties. As of March 31, 2019, we were in compliance with all applicable covenants.

States whether the entity was in compliance with the debt covenants throughout the reporting period, and describes facts and circumstances of any compliance failure.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (g)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 944
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