Restructuring and Related Charges - Summary of Restructuring and Related Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	$ 72.6	$ 65.7	$ 75.6
Global productivity improvement program
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	71.6	60.9	0.0
HHI distribution center consolidation
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	0.0	2.3	52.0
GPC rightsizing initiative
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	0.0	0.0	12.1
Other restructuring activities
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	1.0	2.5	11.5
Cost of goods sold
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	14.3	2.8	3.6
Operating expense
Restructuring Cost and Reserve [Line Items]
Restructuring and related charges	$ 58.3	$ 62.9	$ 72.0