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Intangible assets and goodwill (Details 2)
 12 Months Ended
Dec. 31, 2019
Bottom of range [member] | Mining property, water rights and rights of way [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill Indefinite
Bottom of range [member] | Mining property [member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 1 year
Bottom of range [member] | Intellectual property rights, patents and other industrial property rights, service [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 1 year
Bottom of range [member] | Commercial trademarks [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 1 year
Bottom of range [member] | IT programs [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 2 years
Top of range [member] | Mining property, water rights and rights of way [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill Indefinite
Top of range [member] | Mining property [member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 11 years
Top of range [member] | Intellectual property rights, patents and other industrial property rights, service [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 16 years
Top of range [member] | Commercial trademarks [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 5 years
Top of range [member] | IT programs [Member]  
Disclosure Of Intangible Assets And Goodwill [Line Items]  
Useful lives or amortisation rates, intangible assets other than goodwill 6 years