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Share-Based Compensation - Summary of Phantom and Incentive Unit Awards Activity (Details) - Phantom and Incentive Unit Awards - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Shares or Units      
Non-vested at the beginning of the period (in shares) 2,953,947 2,664,438  
Granted (in shares) 1,236,322 1,713,192  
Vested (in shares) (1,140,423) (1,062,382)  
Forfeited (in shares) (617,773) (361,301)  
Non-vested at the end of the period (in shares) 2,432,073 2,953,947  
Weighted- Average Grant-Date Fair Value (Per Share or Unit)      
Non-vested at the beginning of the period (in dollars per share) $ 8.97 $ 10.76  
Granted (in dollars per share) 16.11 8.52  
Vested (in dollars per share) 9.74 11.62  
Forfeited (in dollars per share) 9.39 12.29  
Non-vested at the end of the period (in dollars per share) $ 12.13 $ 8.97  
Aggregate Intrinsic Value $ 24 $ 33 $ 24