Goodwill and intangible assets - Schedule of Goodwill (Details) - 6 months ended Mar. 31, 2024 € in Millions, $ in Millions	USD ($)	EUR (€)
Goodwill [Roll Forward]
Beginning balance	$ 1,016.2
Cumulative translation adjustment	5.4
Ending balance	1,022.3
APS Battery Manufacturing Assets
Goodwill [Roll Forward]
Goodwill acquired during period | €		€ 0.7
Batteries & Lights
Goodwill [Roll Forward]
Beginning balance	882.0
Cumulative translation adjustment	5.4
Ending balance	888.1
Batteries & Lights | APS Battery Manufacturing Assets
Goodwill [Roll Forward]
Goodwill acquired during period | €		0.7
Auto Care
Goodwill [Roll Forward]
Beginning balance	134.2
Cumulative translation adjustment	0.0
Ending balance	$ 134.2
Auto Care | APS Battery Manufacturing Assets
Goodwill [Roll Forward]
Goodwill acquired during period | €		€ 0.0