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Stock Based Compensation Performance Shares Activity (Details) - Performance Shares [Member] - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options $ 11.8      
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 2 years      
EBITDA Award [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Beginning balance 0.5 0.3 0.2  
Performance shares granted 0.2 0.2 0.1  
Performance shares vested (0.1) 0.0 0.0  
Performance shares canceled 0.0 0.0 0.0  
Ending balance 0.6 0.5 0.3  
Weighted-average grant date fair value outstanding $ 33.91 $ 30.19 $ 32.27 $ 27.66
Weighted-average grant date fair value granted 39.01 28.04 37.68  
Weighted-average grant date fair value vested 27.73 0 0  
Weighted-average grant date fair value canceled $ 0 $ 0 $ 0  
Total Shareholder Return (TSR) Awards [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]        
Beginning balance 0.5 0.3 0.2  
Performance shares granted 0.2 0.2 0.1  
Performance shares vested (0.1) 0.0 0.0  
Performance shares canceled 0.0 0.0 0.0  
Ending balance 0.6 0.5 0.3  
Weighted-average grant date fair value outstanding $ 20.93 $ 19.55 $ 25.77 $ 21.11
Weighted-average grant date fair value granted 24.58 13.16 31.22  
Weighted-average grant date fair value vested 22.78 0 0  
Weighted-average grant date fair value canceled $ 0 $ 0 $ 0