Financial instruments and financial risk factors - Commodity Pricing Adjustments (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024 USD ($) $ / t T	Dec. 31, 2023 USD ($) $ / t T
Cobalt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Metric tonnes subject to fair value pricing adjustments | T	1,124.7	2,313
10% increase in prices	$ 0.1	$ 0.2
10% decrease in prices	$ (0.1)	$ (0.2)
Market price per tonne | $ / t	27,778	28,660
Nickel
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Metric tonnes subject to fair value pricing adjustments | T	1,124.7	2,313
10% increase in prices	$ 0.1	$ 0.3
10% decrease in prices	$ (0.1)	$ (0.3)
Market price per tonne | $ / t	16,525	16,250