Goodwill and intangible assets - Schedule of Goodwill (Details) $ in Millions	6 Months Ended
Mar. 31, 2021 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 1,016.0
Cumulative translation adjustment	12.3
Ending balance	1,057.5
Americas
Goodwill [Roll Forward]
Beginning balance	865.8
Cumulative translation adjustment	0.4
Ending balance	895.4
International
Goodwill [Roll Forward]
Beginning balance	150.2
Cumulative translation adjustment	11.9
Ending balance	162.1
Formulations Acquisition
Goodwill [Roll Forward]
Goodwill acquired	29.2
Formulations Acquisition \| Americas
Goodwill [Roll Forward]
Goodwill acquired	29.2
Formulations Acquisition \| International
Goodwill [Roll Forward]
Goodwill acquired	$ 0.0

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(1))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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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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