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GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - REVENUE RECOGNITION (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Accounting Policies [Abstract] |  |
Travel credits for future travel | $ 106 | $ 62

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- Definition Travel credits for future travel + References No definition available. + Details
Name: | alk_TravelCreditsForFutureTravel
Namespace Prefix: | alk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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