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Stockholders' Equity and Share-Based Awards - Summary of Changes In Stock Options (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Stock Based Compensation [Abstract]        
Weighted Average Exercise Price Per Share, Outstanding, Beginning of Period $ 15   $ 15 $ 16
Outstanding Shares, Beginning of Period 0.4      
Outstanding Shares, Exercised (0.1)      
Outstanding Shares, End of Period 0.3      
Weighted Average Exercise Price Per Share, Exercised $ 18      
Weighted Average Exercise Price Per Share, Outstanding, End of Period $ 15      
Weighted Average Remaining Life, Outstanding, End of Period 2 years 2 months 12 days      
Aggregate Intrinsic Value, Outstanding     $ 0.0  
Aggregate Intrinsic Value, Exercisable   $ 1.2