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Pension and Other Postretirement Plans - Participation in the IAM National Pension Plan (Details) - IAM National Pension Plan - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Multiemployer Plans [Line Items]
Plan length	10 years
Additional contribution as a percentage of the hourly contribution rate	0.025%
Surcharge imposed	No
United Airlines, Inc.
Multiemployer Plans [Line Items]
Contributions	$ 53	$ 59	$ 52

X

- Definition

Multiemployer Plan, Additional Contribution Rate In Excess Of The Hourly Contribution Rate

+ References

No definition available.

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- Definition

Multiemployer Plan, Plan Term

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- Definition

Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan.

+ References

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-Publisher FASB
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- Definition

Indicates whether employer paid surcharge to multiemployer pension plan determined to be individually significant. Acceptable values are "No", "Yes" and "NA".

+ References

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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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