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Asset retirement obligations - Summary of present value of estimated future net cash outflows (Details)
Dec. 31, 2020
Dec. 31, 2019
Turkey    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate   180.00%
Discount rate   190.00%
Turkey | Bottom of range    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 0.70%  
Discount rate 0.70%  
Turkey | Top of range    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 1.50%  
Discount rate 1.50%  
Canada    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 90.00% 180.00%
Discount rate 90.00% 190.00%
Romania    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 150.00% 190.00%
Discount rate 150.00% 230.00%
Greece | Bottom of range    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 0.40% 1.70%
Discount rate 0.40% 1.70%
Greece | Top of range    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 1.70% 1.90%
Discount rate 1.70% 2.30%
Brazil    
Disclosure of Asset Retirement Obligations [line items]    
Inflation rate 0.00% 160.00%
Discount rate 0.00% 160.00%