Restructuring and related charges - Summarization of Restructuring and Related Charges (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 15.2	$ 28.7	$ 22.9
Consumer products cost of goods sold classification
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.5	2.1	3.7
Selling, acquisition, operating and general expenses classification
Restructuring Cost and Reserve [Line Items]
Restructuring charges	14.7	26.6	19.2
Global Cost Reduction Initiatives
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5.2	$ 17.1	13.4
Total Projected Costs	20.0
Expected Completion Date		Sep. 30, 2017
HHI Business Rationalization Initiatives [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.8	$ 10.3	4.5
Expected Completion Date		Sep. 30, 2016
Global Expense Rationalization Initiatives
Restructuring Cost and Reserve [Line Items]
Restructuring charges	5.3	$ 0.0	0.0
Expected Completion Date		Sep. 30, 2016
Other initiatives
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2.9	$ 1.3	$ 5.0