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Share Capital and Earnings Per Share - Summary of Reconciliation of Denominator (Number of Shares) in Calculation of Basic and Diluted Earnings Per Share (Detail) - shares
shares in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Earnings per share [abstract]    
Weighted average number of common shares (in millions) 1,978 1,973
Dilutive stock-based awards(in millions) 8 4
Weighted average number of diluted common shares (in millions) 1,986 1,977