Name:	ual_DefinedBenefitPlanNetPeriodicBenefitCostCreditGainLossDueToSpecialAndContractualTerminationBenefits
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Gain (Loss) On Financial Instruments, Non-Operating

No definition available.

Name:	ual_GainLossOnFinancialInstrumentsNonOperating
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Gain (Loss) On Net Charges

No definition available.

Name:	ual_GainLossOnNetCharges
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of gain (loss) on sale of other assets and other miscellaneous charges.

No definition available.

Name:	ual_GainLossOnSaleOfOtherAssetsAndOtherMiscellaneousCharges
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Grant Income

No definition available.

Name:	ual_GrantIncome
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Labor Contract Ratification Bonus

No definition available.

Name:	ual_LaborContractRatificationBonus
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Loss Contingency, Contract Disputes

No definition available.

Name:	ual_LossContingencyContractDisputes
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Number of Aircraft and Related Spare Engines Retired

No definition available.

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

Number of Aircraft Held for Sale

No definition available.

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

Proceeds From Government Assistance

No definition available.

Name:	ual_ProceedsFromGovernmentAssistance
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Restructuring And Related Cost, Number Of Employees Voluntarily Separated

No definition available.

Name:	ual_RestructuringAndRelatedCostNumberOfEmployeesVoluntarilySeparated
Namespace Prefix:	ual_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Restructuring Programs, One-Time Contribution Per Employee

No definition available.

Name:	ual_RestructuringProgramsOneTimeContributionPerEmployee
Namespace Prefix:	ual_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Special Charges [Line Items]

No definition available.

Name:	ual_SpecialChargesLineItems
Namespace Prefix:	ual_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482130/360-10-45-4

Name:	us-gaap_AssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

Gross amount of debt extinguished.

No definition available.

Name:	us-gaap_ExtinguishmentOfDebtAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69C

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-4

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The amount of loss pertaining to the specified contingency that was charged against earnings in the period, including the effects of revisions in previously reported estimates.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483076/450-20-50-1

Name:	us-gaap_LossContingencyLossInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Period expense related to postemployment benefits.

No definition available.

Name:	us-gaap_PostemploymentBenefitsPeriodExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-14

Name:	us-gaap_ProceedsFromIssuanceOfUnsecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The cash inflow from issuance of rights to purchase common shares at predetermined price (usually issued together with corporate debt).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 14
-Subparagraph (a)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-14

Name:	us-gaap_ProceedsFromIssuanceOfWarrants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of cash outflow for short-term and long-term debt. Excludes payment of lease obligation.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-15

Name:	us-gaap_RepaymentsOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Name:	us-gaap_WriteOffOfDeferredDebtIssuanceCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	srt_AircraftTypeAxis=ual_AirbusA319Boeing737700Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_AircraftTypeAxis=ual_AirbusA319sMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_AircraftTypeAxis=ual_Boeing737700Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_AircraftTypeAxis=ual_EmbraerEMB145LRMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_EmployeeSeveranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RestructuringPlanAxis=ual_VoluntarySeparationLeaveVSLProgramsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ual_EmployeeClassificationAxis=ual_FullTimeEmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ual_EmployeeClassificationAxis=ual_PartTimeEmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ClassOfWarrantOrRightAxis=ual_PayrollSupportProgram23PSP23WarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DebtInstrumentAxis=ual_PayrollSupportProgram2And3PSP23NoteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: