Restructuring and related charges - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	$ 67.8
Restructuring charges	62.5	$ 15.2	$ 28.7
Consumer products cost of goods sold classification
Restructuring Cost and Reserve [Line Items]
Restructuring charges	18.3	0.5	2.1
Selling, acquisition, operating and general expenses classification
Restructuring Cost and Reserve [Line Items]
Restructuring charges	44.2	14.7	26.6
Pet Rightsizing Initiative [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	8.2
Restructuring and Related Cost, Expected Cost	11.0
Restructuring charges	8.2	0.0	0.0
HHI Business Rationalization Initiatives [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date		16.6
Restructuring charges	0.0	$ 1.8	10.3
Expected Completion Date		Sep. 30, 2016
HHI Distribution Center Consolidation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	27.4
Restructuring and Related Cost, Expected Cost	50.0
Restructuring charges	27.4	$ 0.0	0.0
Global Expense Rationalization Initiatives
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	29.5	47.0
Restructuring and Related Cost, Expected Cost	32.0
Restructuring charges	$ 0.0	$ 5.2	$ 17.1
Expected Completion Date		Sep. 30, 2016