Pension and Other Postretirement Plans - Allocation of Plan Assets (Details) - United Airlines, Inc.	12 Months Ended
Dec. 31, 2021
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	10.00%
Equity securities \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	30.00%
Equity securities \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	45.00%
Fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	4.00%
Fixed-income securities \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	35.00%
Fixed-income securities \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	50.00%
Alternatives
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return	7.00%
Alternatives \| Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	15.00%
Alternatives \| Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of total	25.00%

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920

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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.

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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