Debt and Other Obligations - Schedule of Long-term Debt (Details) $ in Millions	Jun. 30, 2025 USD ($) aircraft	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Long-term debt	$ 2,511.1	$ 2,210.5
Less current maturities, net	121.0	436.3
Less unamortized discounts, net	148.0	13.2
Total	$ 2,242.1	1,761.0
Aircraft
Debt Instrument [Line Items]
Failed aircraft sale leaseback \| aircraft	18
Term Loan \| DIP Facility
Debt Instrument [Line Items]
Long-term debt	$ 0.0	$ 309.0
Weighted-average interest rate		11.82%
Fixed-rate loans due through 2039
Debt Instrument [Line Items]
Long-term debt	$ 880.2	$ 972.2
Weighted-average interest rate	5.24%	6.44%
Unsecured term loans due in 2031 \| Payroll Support Program, CARES Act
Debt Instrument [Line Items]
Long-term debt	$ 136.3	$ 136.3
Weighted-average interest rate	2.50%	1.00%
Enhanced Equipment Trust Certificate \| 2015-1 EETC Class A
Debt Instrument [Line Items]
Long-term debt	$ 223.6	$ 234.6
Weighted-average interest rate	4.04%	4.10%
Enhanced Equipment Trust Certificate \| 2017-1 EETC Class AA
Debt Instrument [Line Items]
Long-term debt	$ 154.3	$ 160.3
Weighted-average interest rate	3.36%	3.38%
Enhanced Equipment Trust Certificate \| 2017-1 EETC Class A
Debt Instrument [Line Items]
Long-term debt	$ 51.4	$ 53.4
Weighted-average interest rate	3.63%	3.65%
Enhanced Equipment Trust Certificate \| 2017-1 EETC Class B
Debt Instrument [Line Items]
Long-term debt	$ 0.0	$ 44.7
Weighted-average interest rate		3.80%
Enhanced Equipment Trust Certificate \| 2025 EETC Class B(R)
Debt Instrument [Line Items]
Long-term debt	$ 215.0	$ 0.0
Weighted-average interest rate	11.00%
Exit secured notes \| 2030 Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 850.3	0.0
Weighted-average interest rate	12.00%
Revolving credit facility \| Revolving credit facility due in 2028
Debt Instrument [Line Items]
Long-term debt	$ 0.0	$ 300.0
Weighted-average interest rate		6.67%

Debt Instrument, (Unamortized Discount), Net Of Fresh Start Accounting Original Issue Discount Fair Value Adjustment

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- Definition

Sale Leaseback Transaction, Failed, Number

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as current. Excludes lease obligation.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

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Weighted average interest rate of long-term debt outstanding calculated at point in time.

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