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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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

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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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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Fair Value Measurements - Long-term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Apr. 30, 2021	May 12, 2020
Debt Instrument [Line Items]
Carrying Value	$ 3,355.0	$ 3,642.4
Secured Debt \| 8.00% senior secured notes
Debt Instrument [Line Items]
Stated interest rate percentage	8.00%	8.00%	8.00%
Carrying Value	$ 1,110.0	$ 1,110.0
Fixed-rate term loans
Debt Instrument [Line Items]
Carrying Value	994.2	1,094.7
Unsecured term loans \| Unsecured term loans
Debt Instrument [Line Items]
Carrying Value	136.3	136.3
2015-1 EETC Class A
Debt Instrument [Line Items]
Carrying Value	267.6	278.6
2015-1 EETC Class B
Debt Instrument [Line Items]
Carrying Value	44.0	48.0
2015-1 EETC Class C
Debt Instrument [Line Items]
Carrying Value	0.0	63.8
2017-1 EETC Class AA
Debt Instrument [Line Items]
Carrying Value	172.2	186.3
2017-1 EETC Class A
Debt Instrument [Line Items]
Carrying Value	57.4	62.1
2017-1 EETC Class B
Debt Instrument [Line Items]
Carrying Value	48.2	51.7
2017-1 EETC Class C
Debt Instrument [Line Items]
Carrying Value	$ 0.0	$ 85.5
Convertible Notes \| 4.75% convertible notes due 2025
Debt Instrument [Line Items]
Stated interest rate percentage	4.75%	4.75%			4.75%
Carrying Value	$ 25.1	$ 25.4
Convertible Notes \| 1.00% convertible notes due 2026
Debt Instrument [Line Items]
Stated interest rate percentage	1.00%	1.00%		1.00%
Carrying Value	$ 500.0	$ 500.0
Estimated Fair Value
Debt Instrument [Line Items]
Estimated Fair Value	3,107.7	3,355.0
Estimated Fair Value \| Level 3 \| Secured Debt \| 8.00% senior secured notes
Debt Instrument [Line Items]
Estimated Fair Value	1,093.0	1,085.0
Estimated Fair Value \| Level 3 \| Fixed-rate term loans
Debt Instrument [Line Items]
Estimated Fair Value	912.6	1,003.9
Estimated Fair Value \| Level 3 \| Unsecured term loans \| Unsecured term loans
Debt Instrument [Line Items]
Estimated Fair Value	116.9	116.0
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class A
Debt Instrument [Line Items]
Estimated Fair Value	239.3	247.5
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class B
Debt Instrument [Line Items]
Estimated Fair Value	42.9	45.6
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class C
Debt Instrument [Line Items]
Estimated Fair Value	0.0	63.1
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class AA
Debt Instrument [Line Items]
Estimated Fair Value	149.4	161.6
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class A
Debt Instrument [Line Items]
Estimated Fair Value	48.4	52.3
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class B
Debt Instrument [Line Items]
Estimated Fair Value	42.8	44.9
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class C
Debt Instrument [Line Items]
Estimated Fair Value	0.0	85.1
Estimated Fair Value \| Level 2 \| Convertible Notes \| 4.75% convertible notes due 2025
Debt Instrument [Line Items]
Estimated Fair Value	43.1	44.9
Estimated Fair Value \| Level 2 \| Convertible Notes \| 1.00% convertible notes due 2026
Debt Instrument [Line Items]
Estimated Fair Value	$ 419.3	$ 405.1