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Pension and Other Postretirement Plans (Defined Contribution Plans) - Additional Information (Detail) - United Airlines, Inc. - USD ($) $ in Millions	12 Months Ended
	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.

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No definition available.

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

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No definition available.

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- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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No definition available.

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- Details

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