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Stock-Based Compensation - Fair Value of Stock Options Granted and Compensation Expenses (Detail) - CAD / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Risk-free interest rate 0.97% 1.60%
Expected dividend yield 2.00% 2.00%
Expected volatility 26.00% 29.00%
Expected time until exercise 4 years 7 months 6 days 4 years 6 months
Weighted average fair value of options granted in year [Cdn$] CAD 12.84 CAD 11.47