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Share-Based Compensation - Liability-Classified Awards (Details) - Cash restricted stock units - Payable 2021 - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Units (in shares) 13,351  
Fair value $ 0 $ 8
Vested Liability $ 0