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Significant Accounting Policies - Estimated Useful Lives of Property and Equipment (Details) | 12 Months Ended
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Dec. 31, 2021
Aircraft, spare engines and related rotable parts | Minimum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 25 years
Aircraft, spare engines and related rotable parts | Maximum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 30 years
Aircraft seats | Minimum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 10 years
Aircraft seats | Maximum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 15 years
Buildings | Minimum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 25 years
Buildings | Maximum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 45 years
Other property and equipment | Minimum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 3 years
Other property and equipment | Maximum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 15 years
Computer software | Minimum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 5 years
Computer software | Maximum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 15 years
Building improvements | Minimum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 1 year
Building improvements | Maximum |
Property, Plant and Equipment [Line Items] |
Estimated useful life | 40 years

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

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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
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

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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: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_OtherCapitalizedPropertyPlantAndEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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