Goodwill and intangible assets - Schedule of Goodwill (Details) $ in Millions	6 Months Ended
	Mar. 31, 2019 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 244.2
Cumulative translation adjustment	1.2
Ending balance	1,012.4
Unallocated
Goodwill [Roll Forward]
Beginning balance	0.0
Cumulative translation adjustment	1.0
Ending balance	768.0
Americas
Goodwill [Roll Forward]
Beginning balance	228.4
Cumulative translation adjustment	0.0
Ending balance	228.4
International
Goodwill [Roll Forward]
Beginning balance	15.8
Cumulative translation adjustment	0.2
Ending balance	16.0
Spectrum Brands Holdings
Goodwill [Roll Forward]
Goodwill acquired	498.6
Spectrum Brands Holdings | Unallocated
Goodwill [Roll Forward]
Goodwill acquired	498.6
Spectrum Brands Holdings | Americas
Goodwill [Roll Forward]
Goodwill acquired	0.0
Spectrum Brands Holdings | International
Goodwill [Roll Forward]
Goodwill acquired	0.0
Spectrum Auto Care Acquisition
Goodwill [Roll Forward]
Goodwill acquired	268.4
Spectrum Auto Care Acquisition | Unallocated
Goodwill [Roll Forward]
Goodwill acquired	268.4
Spectrum Auto Care Acquisition | Americas
Goodwill [Roll Forward]
Goodwill acquired	0.0
Spectrum Auto Care Acquisition | International
Goodwill [Roll Forward]
Goodwill acquired	$ 0.0