Goodwill and intangible assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 685.4	$ 181.3
Trademarks and trade names - indefinite lived	1,292.6	76.9
Total Other intangible assets, net	1,978.0	258.2
Accumulated Amortization	41.2	25.5
Net Carrying Amount	644.2	155.8
Total Other intangible assets, net	1,936.8	232.7
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	61.0	44.3
Accumulated Amortization	7.8	6.1
Net Carrying Amount	53.2	38.2
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	412.5	99.6
Accumulated Amortization	21.3	13.4
Net Carrying Amount	391.2	86.2
Patents
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.5	34.5
Accumulated Amortization	6.9	5.7
Net Carrying Amount	27.6	28.8
Proprietary technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	174.5
Accumulated Amortization	4.7
Net Carrying Amount	169.8
Proprietary Formula
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2.4	2.4
Accumulated Amortization	0.2	0.1
Net Carrying Amount	2.2	2.3
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