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REVENUE FROM CONTRACTS WITH CUSTOMERS - Contract Liabilities Activity (Details) - Mileage Plan Revenue [Member] - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Change in Contract with Customer, Liability [Roll Forward] |  |
Total Deferred Revenue balance at January 1 | $ 1,726 | $ 1,535
Increase in liability for mileage credits issued | 183 | 185
Total Deferred Revenue balance at March 31 | 1,751 | 1,569
Passenger revenue [Member] |  |
Change in Contract with Customer, Liability [Roll Forward] |  |
Revenue recognized | (139) | (128)
Mileage plan other revenue [Member] |  |
Change in Contract with Customer, Liability [Roll Forward] |  |
Revenue recognized | $ (19) | $ (23)

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- Definition Change in Contract with Customer, Liability [Roll Forward] + References No definition available. + Details
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Namespace Prefix: | alk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Contract with Customer, Liability + References No definition available. + Details
Name: | alk_ContractwithCustomerLiability
Namespace Prefix: | alk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Contract with Customer, Liability, Increase From Issuance of Credits + References No definition available. + Details
Name: | alk_ContractwithCustomerLiabilityIncreaseFromIssuanceofCredits
Namespace Prefix: | alk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Contract with Customer, Liability, Revenue Recognized + References No definition available. + Details
Name: | alk_ContractwithCustomerLiabilityRevenueRecognized
Namespace Prefix: | alk_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | alk_ContractwithCustomerSalesChannelAxis=alk_MileagePlanRevenueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ProductOrServiceAxis=alk_PassengerServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ProductOrServiceAxis=alk_MileagePlanServicesOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |