Convertible debt - Schedule of Total Convertible Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2022	Oct. 31, 2021
Debt Conversion [Line Items]
Convertible debt	$ 288.1	$ 272.8	$ 288.5	$ 100.9
KSP Convertible Notes
Debt Conversion [Line Items]
Convertible debt	99.1	91.4	92.4	100.9
Glencore Convertible Notes
Debt Conversion [Line Items]
Convertible debt	$ 189.0	$ 181.4	$ 196.1	$ 0.0

Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Name:	us-gaap_ConvertibleDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant