Convertible debt - Schedule Of KSP and Glencore Debt Activity (Details) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023	Oct. 31, 2022	Oct. 31, 2021
Principal Of Convertible Note [Roll Forward]
Issuance of convertible notes	$ 0.0	$ 0.0	$ 198.7	$ 98.4
Conversion Feature Of Convertible Debt [Roll Forward]
Fair value gain (loss) on embedded derivatives	(21.4)	(22.1)	(31.3)	1.4
Debt Component [Roll Forward]
Convertible debt	272.8	288.1	288.5	100.9
KSP Convertible Notes
Conversion Feature Of Convertible Debt [Roll Forward]
Conversion feature at beginning of period	9.1	6.0	29.0	0.0
Conversion feature issued	0.0	0.0	0.0	27.7
Fair value gain (loss) on embedded derivatives	(3.1)	(6.0)	(19.9)	1.3
Conversion feature at end of period	6.0	0.0	9.1	29.0
Debt Component [Roll Forward]
Debt component at beginning of the period	83.3	85.4	71.9	0.0
Debt component issued	4.3	9.1	5.9	72.3
Transaction costs	0.0	0.0	0.0	(1.6)
Accrued interest paid in kind	(4.3)	(9.1)	(5.9)	0.0
Accrued interest expense	2.1	13.7	11.4	1.2
Debt component at end of period	85.4	99.1	83.3	71.9
Convertible debt	91.4	99.1	92.4	100.9
KSP Convertible Notes | Convertible Debt
Principal Of Convertible Note [Roll Forward]
Principal of convertible note at beginning of period	105.9	110.2	100.0	100.0
Issuance of convertible notes	4.3	9.1	5.9	0.0
Principal of convertible notes at end of the period	110.2	119.3	105.9	100.0
Glencore Convertible Notes
Principal Of Convertible Note [Roll Forward]
Principal of convertible notes at end of the period		225.3
Conversion Feature Of Convertible Debt [Roll Forward]
Conversion feature at beginning of period	34.8	16.5	0.0	0.0
Conversion feature issued	0.0	0.0	46.2	0.0
Fair value gain (loss) on embedded derivatives	(18.3)	(16.1)	(11.4)	0.0
Conversion feature at end of period	16.5	0.4	34.8	0.0
Debt Component [Roll Forward]
Debt component at beginning of the period	161.3	164.9	0.0	0.0
Debt component issued	8.1	17.2	153.8	0.0
Transaction costs	0.0	0.0	(1.3)	0.0
Accrued interest paid in kind	(8.1)	(17.2)	0.0	0.0
Accrued interest expense	3.6	23.7	8.8	0.0
Debt component at end of period	164.9	188.6	161.3	0.0
Convertible debt	181.4	189.0	196.1	0.0
Glencore Convertible Notes | Convertible Debt
Principal Of Convertible Note [Roll Forward]
Principal of convertible note at beginning of period	200.0	208.1	0.0	0.0
Issuance of convertible notes	8.1	17.2	200.0	0.0
Principal of convertible notes at end of the period	$ 208.1	$ 225.3	$ 200.0	$ 0.0