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Earnings per Share - Additional Information (Detail) - shares
shares in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Earnings Per Share [Abstract]        
Antidilutive options to purchase were excluded from computation of diluted earnings per share (in shares) 2.5 2.7 2.5 3.6