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Share-Based Payments - Weighted Average Assumptions (Details)
12 Months Ended
Dec. 31, 2020
year
$ / shares
Dec. 31, 2019
year
$ / shares
Share-Based Payment Arrangements [Abstract]    
Risk-free interest rate 1.20% 1.80%
Expected volatility 19.20% 19.50%
Expected dividend yield 4.00% 4.00%
Expected life of the option (in years) | year 6.3 6.3
Exercise price (in CAD per share) | $ / shares $ 61.88 $ 50.58