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Variable Interest Entities - Additional Information (Detail) - Variable Interest Entity, Not Primary Beneficiary	Dec. 31, 2017 Aircraft
Mainline
Variable Interest Entity [Line Items]
Aircraft under operating lease, fixed purchase options	38
Regional Carrier
Variable Interest Entity [Line Items]
Aircraft under operating lease	158

X

- Definition

Number of Aircraft under Operating Lease Agreements with Fixed Price Purchase Options

+ References

No definition available.

+ Details

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Namespace Prefix:	ual_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of aircraft under operating lease agreements with purchase options at prices potentially below fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	ual_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

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

X

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=us-gaap_MainlineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ProductOrServiceAxis=us-gaap_RegionalCarrierMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: