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Earnings and Dividends per Share - Additional Information (Detail) - $ / shares
shares in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Aug. 07, 2017
Earnings And Dividends Per Share [Abstract]          
Shares not included in computation of diluted Earning per share 0.8 1.1 0.7 1.4  
Quarterly dividend declared per share         $ 0.075
Dividend payable date     Sep. 29, 2017    
Common Stock, dividends, per share, Paid     $ 0.075