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Financial Instruments and Financial Risk Management - Summary of Provisionally Valued Outstanding Receivable And Payable Positions (Detail)
lb in Millions
 12 Months Ended
Dec. 31, 2018
USD_per_Pound
lb
Dec. 31, 2017
USD_per_Pound
lb
Copper [member]    
Disclosure of fair value of settlement receivables and payables [line items]    
Outstanding receivable 93 138
Commodity price | USD_per_Pound 2.70 3.26
Zinc [member]    
Disclosure of fair value of settlement receivables and payables [line items]    
Outstanding receivable 208 197
Outstanding payable 77 97
Commodity price | USD_per_Pound 1.12 1.50
Lead [member]    
Disclosure of fair value of settlement receivables and payables [line items]    
Outstanding receivable 24 44
Outstanding payable 16 30
Commodity price | USD_per_Pound 0.91 1.13