Goodwill and intangible assets - Schedule of Goodwill (Details) $ in Millions	6 Months Ended
	Mar. 31, 2023 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 1,003.1
Cumulative translation adjustment	16.4
Ending balance	1,019.5
Batteries & Lights
Goodwill [Roll Forward]
Beginning balance	868.9
Cumulative translation adjustment	16.4
Ending balance	885.3
Auto Care
Goodwill [Roll Forward]
Beginning balance	134.2
Cumulative translation adjustment	0.0
Ending balance	$ 134.2

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.