Goodwill and Intangible Assets - Components of Company's Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill (not subject to amortization)	$ 3,147.8	$ 3,160.4	$ 3,218.1
Intangible assets:
Customer relationships, noncompete agreements and other	837.3	848.6	867.0
Trademarks and tradenames	16.5	7.9	0.0
Accumulated amortization	(416.3)	(393.2)	(376.2)
Intangible assets, net (definite-lived)	437.5	463.3	490.8
Trademarks and tradenames (indefinite-lived)	50.8	50.3	136.3
Total intangible assets, net	$ 488.3	$ 513.6	$ 627.1

Finite-Lived Trademarks and Tradenames, Gross

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Gross carrying amount before accumulated amortization as of the balance sheet date to an asset acquired in a business combination representing a favorable existing relationship with customers having a finite beneficial life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Carrying amount (original costs adjusted for previously recognized amortization and impairment) as of the balance sheet date for the rights acquired through registration of a trademark to gain or protect exclusive use of a business name, symbol or other device or style for a projected indefinite period of benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)
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Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

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