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Financial Instruments and Financial Risk Management - Summary of Fair Value of Commodity Swaps Valuation by Discounted Cash Flow Method (Detail)
lb in Millions, $ in Millions
Dec. 31, 2018
CAD ($)
lb
USD_per_LB
Zinc [member]  
Disclosure of fair value of commodity swaps [line items]  
Quantity | lb 122
Fair Value Asset (Liability) | $ $ (6)
Lead [member]  
Disclosure of fair value of commodity swaps [line items]  
Quantity | lb 70
Fair Value Asset (Liability) | $ $ 2
Purchase Commitments [member] | Zinc [member]  
Disclosure of fair value of commodity swaps [line items]  
Average Price 1.14
Purchase Commitments [member] | Lead [member]  
Disclosure of fair value of commodity swaps [line items]  
Average Price 0.90
Sale Commitments [member] | Zinc [member]  
Disclosure of fair value of commodity swaps [line items]  
Average Price 1.11
Sale Commitments [member] | Lead [member]  
Disclosure of fair value of commodity swaps [line items]  
Average Price 0.92