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Pension and Other Postretirement Plans - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Profit sharing and payroll tax expense | $ 0 | $ 491 | $ 334
Minimum |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Percentage of pre-tax earnings paid for profit sharing plan | 5.00% |  |
Maximum |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Percentage of pre-tax earnings paid for profit sharing plan | 20.00% |  |
IAM National Pension Plan |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Multi-employer plan contributions |  | $ 510 |
Percent of company's contribution to plan |  | 10.00% |
United Airlines, Inc. |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Expense for defined contribution plans | $ 687 | $ 735 | 693
United Airlines, Inc. | Minimum |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Employer contribution percentage | 1.00% |  |
United Airlines, Inc. | Maximum |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Employer contribution percentage | 16.00% |  |
Pension Benefits |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Charges for special termination benefits under VSPs | $ 54 | 0 | 0
Payments for defined benefit plan settlements | 1,400 |  |
Settlement losses | 430 |  |
Increase in postretirement benefit liability if there was a 50 basis point decrease in the weighted average discount rate | 800 |  |
Increase in benefits expense if there was a 50 basis point decrease in the weighted average discount rate | 78 |  |
Decrease in expected long-term rate of return on plan assets if there was a 50 basis point decrease in the weighted average discount rate | 25 |  |
Other Postretirement Benefits |  |  |
Defined Benefit Plans And Defined Contribution Plans Disclosures [Line Items] |  |  |
Charges for special termination benefits under VSPs | 201 | $ 0 | $ 0
Increase in postretirement benefit liability if there was a 50 basis point decrease in the weighted average discount rate | 48 |  |
Increase in benefits expense if there was a 50 basis point decrease in the weighted average discount rate | 2 |  |
Expected employer contributions to pension and postretirement plans | $ 82 |  |

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