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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 (Parenthetical) (Detail) - shares
shares in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share based payments arrangements [Member]    
Earnings per share [Line Items]    
Anti-dilutive stock-based awards excluded from the calculation of EPS 2 14