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Allocation of Plan Assets (Detail) - United Airlines, Inc. | 12 Months Ended
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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%

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- 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 + Details
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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
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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 + Details
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