Income taxes - deferred assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Reserves and accrued expenses	$ 61.7	$ 51.6
Pension, postretirement and environmental liabilities	1.1	14.7
Net operating loss and research and development carryforwards	325.7	312.4
Other	6.1	10.2
Deferred tax assets, gross	394.6	388.9
Less: valuation allowances	(179.7)	(187.6)
Deferred tax assets, net	214.9	201.3
Deferred tax liabilities:
Intangibles	(810.4)	(892.8)
Property, plant and equipment	(51.3)	(52.0)
Investment in partnerships	(44.1)	(148.0)
Deferred tax liabilities	(905.8)	(1,092.8)
Net deferred tax liability	(690.9)	(891.5)
Other Assets
Deferred tax assets:
Deferred tax assets, net	40.5	21.5
Deferred Income Tax Charge [Member]
Deferred tax liabilities:
Net deferred tax liability	$ (731.4)	$ (913.0)