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Fair Value Measurements - Balance Sheet Grouping (Details) - USD ($)
$ in Millions
Sep. 30, 2020
Dec. 31, 2019
Current assets: Prepaid expenses and other current assets | Call option    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative assets $ 0 $ 29
Current liabilities: Accounts payable, accrued liabilities and other | Conversion option    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Derivative liabilities $ 0 $ 29