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Allocation of Plan Assets (Detail) - United Airlines, Inc.	12 Months Ended
	Dec. 31, 2017
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	9.50%
Equity Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	27.00%
Equity Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	42.00%
Fixed-Income Securities
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	5.50%
Fixed-Income Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	30.00%
Fixed-Income Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	40.00%
Alternatives
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	7.30%
Alternatives | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	10.00%
Alternatives | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	25.00%
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	7.30%
Other Investments | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	0.00%
Other Investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Percent of Total	10.00%

X

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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+ References

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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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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