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Pension and Other Postretirement Plans (Defined Contribution Plans) - Additional Information (Detail) - United Airlines, Inc. - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, employer | $ 656 | $ 592 | $ 522
Minimum |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contribution, percentage | 1.00% |  |
Maximum |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contribution, percentage | 16.00% |  |

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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 Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Details
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