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Financial Instruments and Financial Risk Management - Schedule of Effect of Change in Commodity Prices on Profit (Loss) (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2018
CAD ($)
USD_per_Pound
Dec. 31, 2017
CAD ($)
USD_per_Pound
Copper [member]    
Disclosure of commodity price risk for financial instruments [line items]    
Commodity price 2.70 3.26
Copper [member] | Commodity Price Risk [member]    
Disclosure of commodity price risk for financial instruments [line items]    
Commodity price 2.70 3.26
Change in Profit (Loss) Attributable to Shareholders | $ $ 21 $ 35
Zinc [member]    
Disclosure of commodity price risk for financial instruments [line items]    
Commodity price 1.12 1.50
Zinc [member] | Commodity Price Risk [member]    
Disclosure of commodity price risk for financial instruments [line items]    
Commodity price 1.12 1.50
Change in Profit (Loss) Attributable to Shareholders | $ $ 7 $ 5