Restructuring and related charges - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	$ 86.0
Restructuring charges	20.4	$ 2.2
Consumer products cost of goods sold classification
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.8	1.1
Selling, acquisition, operating and general expenses classification
Restructuring Cost and Reserve [Line Items]
Restructuring charges	18.6	1.1
Pet Rightsizing Initiative [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	8.8
Restructuring and Related Cost, Expected Cost	9.0
Restructuring charges	0.6	0.0
HHI Distribution Center Consolidation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	42.6
Restructuring and Related Cost, Expected Cost	55.0
Restructuring charges	15.2	$ 0.0
Global Expense Rationalization Initiatives
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	33.6
Restructuring and Related Cost, Expected Cost	$ 35.0

Amount of costs incurred to date for the specified restructuring cost.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

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Amount expected to be recognized in earnings for the specified restructuring cost.

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