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Share-Based Compensation and Equity - Restricted Stock Unit Activity (Details) - Restricted Stock Units [Member] - $ / shares
shares in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Restricted Stock Units      
Unvested, Shares, Beginning balance 2.2    
Forfeited, Shares (0.1)    
Vested, Shares (1.1)    
Granted, Shares 0.9    
Unvested, Shares, Ending balance 1.9 2.2  
Unvested, Weighted-average grant-date fair value, Beginning balance $ 9.99    
Forfeited, Weighted-average grant-date fair value 13.18    
Vested, Weighted-average grant-date fair value 12.55    
Granted, Weighted-average grant-date fair value 10.64 $ 5.05 $ 17.34
Unvested, Weighted-average grant-date fair value, Ending balance $ 8.83 $ 9.99