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LEASES - NARRATIVE (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) aircraft | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Lessee, Lease, Description [Line Items] |  |  |
Sublease Income | $ 14 | $ 13 |
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability | 81 |  |
Operating Lease, Payments | 302 |  |
Rent expense |  |  | $ 619
Lessor, Operating Lease, Lease Not yet Commenced, Assumption and Judgment, Value of Underlying Asset, Amount | $ 453 |  |
Property Subject to Operating Lease [Member] | Airbus |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Operating leases, number of leased assets (in aircraft) | aircraft | 71 |  |
Property Subject to Operating Lease [Member] | Q400 |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Operating leases, number of leased assets (in aircraft) | aircraft | 7 |  |
Property Subject to Operating Lease [Member] | E175 [Member] |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Operating leases, number of leased assets (in aircraft) | aircraft | 32 |  |
Property Subject to Operating Lease [Member] | B737 |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Operating leases, number of leased assets (in aircraft) | aircraft | 10 |  |
Airport Facilities [Member] |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Variable Lease, Cost | $ 286 | 322 |
Aircraft Leases [Member] | Maximum [Member] |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Lessee, Operating Lease, Term of Contract | 11 years |  |
Corporate real estate [Member] |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Variable Lease, Cost | $ 12 | $ 10 |
CPA Aircraft [Member] | Maximum [Member] |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Lessee, Operating Lease, Term of Contract | 10 years |  |
CPA Aircraft [Member] | Minimum [Member] |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Lessee, Operating Lease, Term of Contract | 6 years 6 months |  |

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- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
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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. + References No definition available. + Details
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- Definition Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980 + Details
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- Definition Amount lessor expects from underlying asset following end of operating lease term for lease that has not yet commenced. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 30 -Section 50 -Paragraph 3 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919359-209981 + Details
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- Definition Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918643-209977 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 + Details
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- Definition Amount of increase in right-of-use asset obtained in exchange for operating lease liability. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(2) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 + Details
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- Definition Amount of sublease income excluding finance and operating lease expense. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 + Details
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- Definition Amount of variable lease cost, excluded from lease liability, recognized when obligation for payment is incurred for finance and operating leases. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 + Details
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