Goodwill and intangible assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2024	Sep. 30, 2023
Finite-Lived Intangible Assets [Line Items]
Cumulative translation adjustment	$ 5.4
Gross Carrying Amount	772.9	$ 772.2
Trademarks and trade names - indefinite lived	763.0	762.8
Total Other intangible assets, net	1,535.9	1,535.0
Accumulated Amortization	(326.8)	(297.3)
Net Carrying Amount	446.1	474.9
Total Other intangible assets, net	1,209.1	1,237.7
Trademarks and trade names - indefinite lived
Finite-Lived Intangible Assets [Line Items]
Trademarks and trade names - indefinite lived		762.8
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	142.6	142.4
Accumulated Amortization	(33.4)	(29.4)
Net Carrying Amount	109.2	113.0
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	394.5	394.2
Accumulated Amortization	(153.2)	(139.7)
Net Carrying Amount	241.3	254.5
Patents
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.1	33.9
Accumulated Amortization	(19.4)	(18.2)
Net Carrying Amount	14.7	15.7
Proprietary Technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	172.5	172.5
Accumulated Amortization	(108.8)	(100.0)
Net Carrying Amount	63.7	72.5
Proprietary Formula
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	29.2	29.2
Accumulated Amortization	(12.0)	(10.0)
Net Carrying Amount	$ 17.2	$ 19.2