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Summary of Significant Accounting Policies - Other Investments (Details) - USD ($)
$ in Millions
Jun. 30, 2021
Dec. 31, 2020
Accounting Policies [Abstract]    
Cost method investments - jetblue tech ventures $ 46 $ 40
Measurement alternative, ownership percentage 10.00%  
Cost method investments - TWA flight center hotel $ 14 $ 14