Commitments and Contingencies - Aircraft-Related Commitments and Financing Arrangements (Details) $ in Millions	Dec. 31, 2019 USD ($) aircraft_engine aircraft
Secured Debt
Principal and Interest Commitments
Principal and interest commitments, 2020	$ 9.6
Principal and interest commitments, 2021	12.9
Principal and interest commitments, 2022	13.0
Principal and interest commitments, 2023	13.0
Principal and interest commitments, 2024	13.1
Principal and interest commitments, 2025 and beyond	83.3
Interest Commitments
Interest commitments, 2020	77.9
Interest commitments, 2021	71.0
Interest commitments, 2022	64.7
Interest commitments, 2023	54.6
Interest commitments, 2024	44.0
Interest commitments, 2025 and beyond	118.1
Aircraft and Related Flight Equipment
Committed Expenditures
Committed expenditures, 2020	988.0
Committed expenditures, 2021	744.8
Committed expenditures, 2022	123.7
Committed expenditures, 2023	491.6
Committed expenditures, 2024	1,002.5
Committed expenditures, 2025 and beyond	3,605.4
Non-aircraft Related Commitments
Committed Expenditures
Committed expenditures, 2020	21.9
Committed expenditures, 2021	17.1
Committed expenditures, 2022	17.2
Committed expenditures, 2023	13.7
Committed expenditures, 2024	13.9
Committed expenditures, 2025 and beyond	$ 50.3
V2500 SelectTWO Engine \| 2020-2023
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered \| aircraft_engine	1
PurePower PW1100G-JM Engine \| 2020-2023
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered \| aircraft_engine	4
A320 Family
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered \| aircraft	100
Number of aircraft order conversions \| aircraft	50
Airbus
Unrecorded Unconditional Purchase Obligation [Line Items]
Future aircraft to be received \| aircraft	135
Number of delivered aircraft with secured debt financing commitments \| aircraft	64
Airbus \| 2020
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery \| aircraft	3
Airbus \| 2020-2027
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft without secured financing commitments scheduled for delivery \| aircraft	132
Third Party Lessor \| A320NEO
Unrecorded Unconditional Purchase Obligation [Line Items]
Future aircraft to be received \| aircraft	12
Aircraft Rent Commitments [Abstract]
Aircraft rent commitments, 2020	$ 6.0
Aircraft rent commitments, 2021	34.9
Aircraft rent commitments, 2022	44.1
Aircraft rent commitments, 2023	44.1
Aircraft rent commitments, 2024	44.1
Aircraft rent commitments, 2025 and thereafter	$ 356.1

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Number of Spare Aircraft Engines Ordered

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Number of Aircraft Order Conversions

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Principal And Interest Commitments Related to Future Secured Debt After Year Five

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