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GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - MAINTENANCE DEPOSITS (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Accounting Policies [Abstract] |  |
Aircraft Maintenance Deposits | $ 242 | $ 143

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- Definition Aircraft Maintenance Deposits + References No definition available. + Details
Name: | alk_AircraftMaintenanceDeposits
Namespace Prefix: | alk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration