Business combinations - Preliminary purchase price allocation (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill			$ 2,263.2	$ 2,280.8
Purchase consideration, net of cash				1,814.8
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Purchase price adjustments			$ 7.0
Nexeo Solutions, Inc.
Business Acquisition [Line Items]
Trade accounts receivable, net	$ 296.3	$ 296.3		296.3
Inventories	150.2	150.2		150.2
Prepaid expenses and other current assets	64.2	64.2		65.4
Assets held for sale	888.2	888.2		888.2
Property, plant and equipment, net	262.3	262.3		262.3
Goodwill	562.7	562.7		555.7
Intangible assets, net	138.7	138.7		138.7
Other assets	37.0	37.0		37.4
Trade accounts payable	(137.7)	(137.7)		(137.7)
Other accrued expenses	(144.5)	(144.5)		(145.8)
Liabilities held for sale	(221.5)	(221.5)		(221.5)
Deferred tax liabilities	(10.9)	(10.9)		(4.2)
Other long-term liabilities	(70.2)	(70.2)		$ (70.2)
Purchase consideration, net of cash	1,814.8	1,814.8
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Prepaid expenses and other current assets		(1.2)
Purchase price adjustments	$ 7.0	7.0
Other assets		(0.4)
Other accrued expenses		1.3
Deferred tax liabilities		$ (6.7)