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Stock-Based Compensation Plans, Assumptions Used to Estimate Fair Value of Options Granted (Details) - 2013 Stock Incentive Plan [Member] - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
May 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Nov. 20, 2017
Stock Options [Member]          
Assumptions [Abstract]          
Stock-based compensation expense   $ 77.6      
Stock Options and Stock Appreciation Rights [Member]          
Assumptions [Abstract]          
Expected life of options     5 years 1 month 6 days 4 years 9 months 18 days  
Risk-free interest rate     1.30% 1.60%  
Assumed volatility     49.50% 49.90%  
Expected dividend rate   0.00% 0.00% 0.00%  
Stock Options and Stock Appreciation Rights [Member] | Minimum [Member]          
Assumptions [Abstract]          
Expected life of options   5 years      
Risk-free interest rate   1.90%      
Assumed volatility   41.20%      
Stock Options and Stock Appreciation Rights [Member] | Maximum [Member]          
Assumptions [Abstract]          
Expected life of options   6 years 3 months      
Risk-free interest rate   2.10%      
Assumed volatility   45.80%      
Deferred Stock Units [Member]          
Assumptions [Abstract]          
Expected life of options   1 year 5 months 1 day      
Assumed volatility   51.50%      
Deferred stock units authorized (in shares) 5.5        
Fair value of deferred stock units (in dollars per share) $ 17.20        
Initial public offering share price (in dollars per share) $ 20.00        
Stock-based compensation expense   $ 97.4      
Reclassified amount from "accrued liabilities" to "capital in excess of par value         $ 6.0
Shares reclassified from accrued liabilities to capital in excess of par value (in shares)         0.2