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Capital Stock (Option Grant Assumptions) (Details) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Capital Stock [Abstract]      
Weighted-average fair value per share $ 17.73 $ 22.55 $ 15.80
Risk-free interest rate 1.30% 1.80% 2.10%
Expected dividend yield 1.60% 1.60% 1.80%
Expected stock price volatility 20.50% 25.50% 26.30%
Expected option life (years) 6 years 1 month 7 years 3 months 7 years 1 month