Derecognition of build-to-suit assets and liabilities due to ASU 2016-02

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

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Amount of increase in right-of-use asset obtained in exchange for operating lease liability.

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Amount of sublease income excluding finance and operating lease expense.

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LEASES - NARRATIVE (Details) $ in Millions		12 Months Ended
LEASES - NARRATIVE (Details) $ in Millions	Jan. 01, 2019 USD ($)	Dec. 31, 2019 USD ($) aircraft	Dec. 31, 2018 USD ($) aircraft	Dec. 31, 2017 USD ($)
Lessee, Lease, Description [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 3
Sublease Income		13
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		176
Operating Lease, Payments		$ 347
Rent expense			$ 619	$ 552
Property Subject to Operating Lease [Member] \| Airbus [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft) \| aircraft		61	61
Property Subject to Operating Lease [Member] \| Q400 [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft) \| aircraft		7	9
Property Subject to Operating Lease [Member] \| E175 [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft) \| aircraft		32	32
Property Subject to Operating Lease [Member] \| B737
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft) \| aircraft		10	10
Airport Facilities [Member]
Lessee, Lease, Description [Line Items]
Variable Lease, Cost		$ 322
Aircraft Leases [Member]
Lessee, Lease, Description [Line Items]
Variable Lease, Cost		$ 4
Aircraft Leases [Member] \| Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		12 years
Corporate real estate [Member]
Lessee, Lease, Description [Line Items]
Variable Lease, Cost		$ 10
CPA Aircraft [Member] \| Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		11 years
CPA Aircraft [Member] \| Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		7 years 6 months
Accounting Standards Update 2016-02 [Member]
Lessee, Lease, Description [Line Items]
Derecognition of Build-to-suit Accounting	$ 150
Retained Earnings
Lessee, Lease, Description [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 3