Goodwill and intangible assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Cumulative translation adjustment	$ 12.9
Gross Carrying Amount	663.8	$ 663.8
Trademarks and trade names - indefinite lived	1,365.0	1,363.8
Total Other intangible assets, net	2,028.8	2,027.6
Accumulated Amortization	(82.5)	(68.7)
Net Carrying Amount	581.3	595.1
Total Other intangible assets, net	1,946.3	1,958.9
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	59.7	59.7
Accumulated Amortization	(10.9)	(9.9)
Net Carrying Amount	48.8	49.8
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	394.2	394.2
Accumulated Amortization	(41.0)	(34.3)
Net Carrying Amount	353.2	359.9
Patents
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.5	34.5
Accumulated Amortization	(8.8)	(8.2)
Net Carrying Amount	25.7	26.3
Proprietary technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	172.5	172.5
Accumulated Amortization	(21.1)	(15.7)
Net Carrying Amount	151.4	156.8
Proprietary Formula
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2.4	2.4
Accumulated Amortization	(0.3)	(0.3)
Net Carrying Amount	2.1	2.1
Non-Compete
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0.5	0.5
Accumulated Amortization	(0.4)	(0.3)
Net Carrying Amount	0.1	$ 0.2
International
Finite-Lived Intangible Assets [Line Items]
Cumulative translation adjustment	$ 12.6