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Net Income per Share - Computation of Basic and Diluted EPS (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Numerator:                        
Net income $ (47) $ 42 $ 33 $ 24 $ 30 $ 46 $ 39 $ 28 $ 52 $ 143 $ 62  
Shares outstanding at the beginning of the period (in shares)         55         55 49 46
Weighted-average number of shares issued:                        
Common stock offering (in shares)                 0 3 0  
Convertible senior notes (in shares)                 0 0 1  
Denominator for basic net income per share (in shares)                 55 52 47  
Effect of dilutive securities:                        
Share-based compensation (in shares)                 0 1 0  
Convertible senior notes (in shares)                 0 1 1  
1.125% Warrants (in shares)                 1 2 0  
Denominator for diluted net income per share (in shares)                 56 56 48  
Net income per share:                        
Basic (in dollars per share) $ (0.85) $ 0.77 $ 0.58 $ 0.44 $ 0.54 $ 0.84 $ 0.78 $ 0.58 $ 0.93 $ 2.75 $ 1.33  
Diluted (in dollars per share) $ (0.85) $ 0.76 $ 0.58 $ 0.43 $ 0.52 $ 0.77 $ 0.72 $ 0.56 $ 0.92 $ 2.58 $ 1.29  
1.125% Warrants                        
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]                        
Stated interest rate (as a percent) 1.125%               1.125%      
1.125% Warrants                        
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]                        
Potentially dilutive common shares excluded from calculations                 0 0 13