v3.26.1
Environmental and other provisions (Schedule of changes in provisions) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of other provisions [line items]    
Provisions, beginning balance $ 330.7 $ 344.2
Net additional provisions made 64.1 25.1
Disbursements (17.8) (11.6)
Reduction of obligation to renounce flow-through share expenditures, net of provisions (5.5) (2.0)
Unwinding of discount 11.1 10.5
Effect of change in discount rate (25.9) (22.7)
Effect of foreign exchange 13.5 (20.8)
Effect of change in share price 32.6 8.0
Provisions, ending balance 402.8 330.7
Decommissioning, restoration and similar liabilities [Member]    
Disclosure of other provisions [line items]    
Provisions, beginning balance 296.9 315.4
Net additional provisions made 26.2 14.5
Disbursements (1.7) (2.1)
Reduction of obligation to renounce flow-through share expenditures, net of provisions 0.0 0.0
Unwinding of discount 11.1 10.5
Effect of change in discount rate (25.9) (22.7)
Effect of foreign exchange 11.8 (18.7)
Effect of change in share price 0.0 0.0
Provisions, ending balance 318.4 296.9
Deferred share units [Member]    
Disclosure of other provisions [line items]    
Provisions, beginning balance 12.3 8.7
Net additional provisions made 0.9 1.1
Disbursements (5.4) (1.6)
Reduction of obligation to renounce flow-through share expenditures, net of provisions 0.0 0.0
Unwinding of discount 0.0 0.0
Effect of change in discount rate 0.0 0.0
Effect of foreign exchange 0.7 (1.1)
Effect of change in share price 13.0 5.2
Provisions, ending balance 21.5 12.3
Restricted share units [Member]    
Disclosure of other provisions [line items]    
Provisions, beginning balance 9.6 5.0
Net additional provisions made 11.5 5.6
Disbursements (6.3) (2.2)
Reduction of obligation to renounce flow-through share expenditures, net of provisions 0.0 0.0
Unwinding of discount 0.0 0.0
Effect of change in discount rate 0.0 0.0
Effect of foreign exchange 0.3 (0.5)
Effect of change in share price 11.0 1.7
Provisions, ending balance 26.1 9.6
Performance share units [Member]    
Disclosure of other provisions [line items]    
Provisions, beginning balance 5.5 2.6
Net additional provisions made 16.0 3.1
Disbursements (3.5) (0.9)
Reduction of obligation to renounce flow-through share expenditures, net of provisions 0.0 0.0
Unwinding of discount 0.0 0.0
Effect of change in discount rate 0.0 0.0
Effect of foreign exchange 0.3 (0.4)
Effect of change in share price 8.6 1.1
Provisions, ending balance 26.9 5.5
Other [Member]    
Disclosure of other provisions [line items]    
Provisions, beginning balance 6.4 12.5
Net additional provisions made 9.5 0.8
Disbursements (0.9) (4.8)
Reduction of obligation to renounce flow-through share expenditures, net of provisions (5.5) (2.0)
Unwinding of discount 0.0 0.0
Effect of change in discount rate 0.0 0.0
Effect of foreign exchange 0.4 (0.1)
Effect of change in share price 0.0 0.0
Provisions, ending balance $ 9.9 $ 6.4