v3.26.1
Revenue and expenses (Narrative) (Details)
$ in Millions
 12 Months Ended
Jan. 09, 2026
USD ($)
Dec. 31, 2025
USD ($)
Share
Dec. 31, 2024
USD ($)
Share
Apr. 12, 2025
USD ($)
Revenue and Expenses [Line Items]        
Variable consideration adjustment   $ 9.9 $ (3.8)  
Stock options granted | Share   828,720 902,874  
Employee share purchase plan, matching contribution, percentage   75.00% 75.00%  
Past service costs   $ 0.0 $ 4.3  
Other expenses   7.8 57.4  
Insurance recovery   25.0    
Write-down/loss on disposal of PP&E   3.5 27.4  
Impairment reversal   $ 322.3 $ 0.0  
Manitoba [Member]        
Revenue and Expenses [Line Items]        
Profit sharing plan, percentage   10.00% 10.00%  
Past service costs   $ 4.3  
Other expenses   $ (8.8) $ 15.8  
Peru [Member]        
Revenue and Expenses [Line Items]        
Profit sharing plan, percentage   8.00% 8.00%  
Other expenses   $ 16.2 $ 15.7  
Arizona [Member]        
Revenue and Expenses [Line Items]        
Other expenses   0.9 8.3  
Write-down/loss on disposal of PP&E     8.1  
Recoverable amount of CGU       $ 2,000.0
Recoverable amount in excess of carrying value       $ 784.4
Impairment reversal   $ 322.3    
British Columbia [Member]        
Revenue and Expenses [Line Items]        
Write-down/loss on disposal of PP&E     7.2  
Loss on replacement and disposal of equipment     $ 7.8  
Bottom of range [Member]        
Revenue and Expenses [Line Items]        
Employee share purchase plan, contributions, percentage of pre-tax base salary   1.00% 1.00%  
Top of range [Member]        
Revenue and Expenses [Line Items]        
Employee share purchase plan, contributions, percentage of pre-tax base salary   10.00% 10.00%  
Wildfire evacuation costs [Member]        
Revenue and Expenses [Line Items]        
Other expenses   $ 4.4 $ 0.0  
Care & maintenance - Manitoba [Member]        
Revenue and Expenses [Line Items]        
Other expenses   13.2 $ 14.6  
Copper World, Inc [Member] | Mitsubishi Corporation [Member] | Events after reporting period [Member]        
Revenue and Expenses [Line Items]        
Percentage of non-controlling interest 30.00%      
Proceeds from sale of minority interest $ 420.0      
Future proceeds from sale of minority interest $ 180.0      
Harmony Gold (Australia) PTY Limited [Member]        
Revenue and Expenses [Line Items]        
Consideration received from sale of non-core project   $ 14.9