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GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - PROPERTY, EQUIPMENT AND DEPRECIATION (Details) | 12 Months Ended
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Dec. 31, 2019
Buildings [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 0.00%
Buildings [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 25 years
Buildings [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 30 years
Minor building and land improvements [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years
Property, Plant, and Equipment, Salvage Value, Percentage | 0.00%
Leaseholds and Leasehold Improvements [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 0.00%
Leaseholds and Leasehold Improvements [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 10.00%
Computer hardware and software [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 0.00%
Computer hardware and software [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 3 years
Computer hardware and software [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years
Other furniture and equipment [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 0.00%
Other furniture and equipment [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 5 years
Other furniture and equipment [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years
B737 | Aircraft [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 10.00%
B737 | Aircraft [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 20 years
B737 | Aircraft [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 25 years
Airbus [Member] | Aircraft [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 10.00%
Airbus [Member] | Aircraft [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 20 years
Airbus [Member] | Aircraft [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 25 years
E175 [Member] | Aircraft [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant, and Equipment, Salvage Value, Percentage | 10.00%
E175 [Member] | Aircraft [Member] | Minimum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 20 years
E175 [Member] | Aircraft [Member] | Maximum [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 25 years
Q400 [Member] | Aircraft [Member] |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 15 years
Property, Plant, and Equipment, Salvage Value, Percentage | 10.00%

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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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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentSalvageValuePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=alk_MinorBuildingAndLandImprovementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LeaseholdsAndLeaseholdImprovementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_TechnologyEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_OfficeEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_AircraftTypeAxis=srt_B737Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=alk_AircraftMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_AircraftTypeAxis=alk_AirbusMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_AircraftTypeAxis=alk_E175Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_AircraftTypeAxis=alk_Q400Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |