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Summary of Significant Accounting Policies Aircraft Maintenance and Repair Costs (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
A320 Series Engine      
Servicing Asset at Amortized Cost [Line Items]      
Deferred Costs for Heavy Maintenance $ 23.3 $ 12.8  
Amortization of Other Deferred Charges 21.0 17.6  
Airbus A320 Aircraft Series      
Servicing Asset at Amortized Cost [Line Items]      
Deferred Costs for Heavy Maintenance 39.0 22.6  
Amortization of Other Deferred Charges $ 21.1 $ 19.9 $ 14.9