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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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.

+ Details

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Fair Value Measurements - Long-term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Apr. 30, 2021	May 12, 2020
Debt Instrument [Line Items]
Carrying Value	$ 3,512.5	$ 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	1,061.9	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	278.6	278.6
2015-1 EETC Class B
Debt Instrument [Line Items]
Carrying Value	48.0	48.0
2015-1 EETC Class C
Debt Instrument [Line Items]
Carrying Value	63.8	63.8
2017-1 EETC Class AA
Debt Instrument [Line Items]
Carrying Value	179.2	186.3
2017-1 EETC Class A
Debt Instrument [Line Items]
Carrying Value	59.7	62.1
2017-1 EETC Class B
Debt Instrument [Line Items]
Carrying Value	49.9	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	3,290.2	3,355.0
Estimated Fair Value \| Level 3 \| Secured Debt \| 8.00% senior secured notes
Debt Instrument [Line Items]
Estimated Fair Value	1,104.1	1,085.0
Estimated Fair Value \| Level 3 \| Fixed-rate term loans
Debt Instrument [Line Items]
Estimated Fair Value	996.8	1,003.9
Estimated Fair Value \| Level 3 \| Unsecured term loans \| Unsecured term loans
Debt Instrument [Line Items]
Estimated Fair Value	121.9	116.0
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class A
Debt Instrument [Line Items]
Estimated Fair Value	251.4	247.5
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class B
Debt Instrument [Line Items]
Estimated Fair Value	46.0	45.6
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class C
Debt Instrument [Line Items]
Estimated Fair Value	63.8	63.1
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class AA
Debt Instrument [Line Items]
Estimated Fair Value	158.1	161.6
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class A
Debt Instrument [Line Items]
Estimated Fair Value	51.2	52.3
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class B
Debt Instrument [Line Items]
Estimated Fair Value	44.1	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	41.7	44.9
Estimated Fair Value \| Level 2 \| Convertible notes \| 1.00% convertible notes due 2026
Debt Instrument [Line Items]
Estimated Fair Value	$ 411.1	$ 405.1