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Non-Controlling Interests - Summary of Information About Subsidiaries with Non-controlling Interests and Non-controlling Interest Balances (Detail) - CAD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2017
Disclosure of subsidiaries [line items]      
Non controlling interests $ 134 $ 142 $ 159
Carmen de Andacollo [member]      
Disclosure of subsidiaries [line items]      
Percentage of Interest and Voti Principal Place of Business by Non-Controll Region IV, Chile    
Ownership ng Rights Held ingInterest 10.00%    
Non controlling interests $ 32 34  
Quebrada Blanca [member]      
Disclosure of subsidiaries [line items]      
Percentage of Interest and Voti Principal Place of Business by Non-Controll Region I, Chile    
Ownership ng Rights Held ingInterest 10.00%    
Non controlling interests $ 10 30  
Elkview Mine Limited Partnership [member]      
Disclosure of subsidiaries [line items]      
Percentage of Interest and Voti Principal Place of Business by Non-Controll British Columbia, Canada    
Ownership ng Rights Held ingInterest 5.00%    
Non controlling interests $ 59 53  
Compania Minera Zafranal S.A.C. [member]      
Disclosure of subsidiaries [line items]      
Percentage of Interest and Voti Principal Place of Business by Non-Controll Arequipa Region, Peru    
Ownership ng Rights Held ingInterest 20.00%    
Non controlling interests $ 33 $ 25