Goodwill and intangible assets (Schedule of Finite-Lived Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Remaining life (in years)	10 years 3 months 18 days
Gross Carrying Amount	$ 663.8	$ 181.3
Accumulated Amortization	(68.7)	(25.5)
Net Carrying Amount	595.1	155.8
Trademarks and trade names - indefinite lived	1,363.8	76.9
Gross Carrying Amount	2,027.6	258.2
Net Carrying Amount	1,958.9	232.7
Trademarks
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	59.7	44.3
Accumulated Amortization	(9.9)	(6.1)
Net Carrying Amount	49.8	38.2
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	394.2	99.6
Accumulated Amortization	(34.3)	(13.4)
Net Carrying Amount	359.9	86.2
Patents
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.5	34.5
Accumulated Amortization	(8.2)	(5.7)
Net Carrying Amount	26.3	28.8
Proprietary formulas
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	172.5	2.4
Accumulated Amortization	(15.7)	(0.1)
Net Carrying Amount	156.8	2.3
Proprietary technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2.4
Accumulated Amortization	(0.3)
Net Carrying Amount	2.1
Non-Compete
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0.5	0.5
Accumulated Amortization	(0.3)	(0.2)
Net Carrying Amount	$ 0.2	$ 0.3