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Income Taxes - Additional Information (Detail) - CAD
CAD in Millions
 12 Months Ended
Jan. 01, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Income Taxes [line items]        
Statutory tax rate     26.10% 26.10%
Unrecognized deferred tax liabilities     CAD 694.0 CAD 730.0
Net operating loss carryforwards     CAD 3,630.0 4,570.0
Loss carryforwards expiration, start year     2028  
Loss carryforwards expiration, end year     2036  
Cumulative Canadian development expenses     CAD 981.0 1,330.0
Development expenses deductible percentage     30.00%  
Federal investment tax credits     CAD 103.7  
Investment tax credits, start year     2021  
Investment tax credits, end year     2037  
United States [member]        
Disclosure of Income Taxes [line items]        
Statutory tax rate     35.00%  
Changes in tax rates or tax laws enacted or announced [member]        
Disclosure of Income Taxes [line items]        
Increase in tax rate 1.00%      
Increase in deferred tax liabilities     CAD 82.0  
Changes in tax rates or tax laws enacted or announced [member] | United States [member]        
Disclosure of Income Taxes [line items]        
Statutory tax rate   21.00%    
Reduction in deferred tax liabilities     101.0  
Unused Tax Credits [member]        
Disclosure of Income Taxes [line items]        
Unrecognized deferred tax assets     CAD 231.0 CAD 270.0