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Pension and Other Postretirement Plans - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |  |  |
Profit sharing and payroll tax expense | $ 491 | $ 334 | $ 349
Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of pre-tax earnings paid for profit sharing plan | 5.00% |  |
Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percentage of pre-tax earnings paid for profit sharing plan | 20.00% |  |
IAM National Pension Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Multi-employer plan contributions |  | $ 467 |
Percent of company's contribution to plan |  | 5.00% |
United Airlines, Inc. |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Expense for defined contribution plans | $ 735 | $ 693 | $ 656
United Airlines, Inc. | Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contribution percentage | 1.00% |  |
United Airlines, Inc. | Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contribution percentage | 16.00% |  |
Retiree Medical Benefit Program |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 3.39% |  |
Decrease in projected benefit obligation due to plan amendment and remeasurement | $ 421 |  |
Accumulated other comprehensive loss prior service | 597 |  |
Actuarial loss net periodic benefit cost | $ 176 |  |
Participants in retiree medical benefit program, year | 7 years |  |
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 3.52% | 4.20% |
Increase in pension benefit liability if there was a 50 basis point decrease in the weighted average discount rate | $ 700 |  |
Increase in benefits expense if there was a 50 basis point decrease in the weighted average discount rate | 69 |  |
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 | 20 |  |
Expected employer contributions to pension and postretirement plans | $ 314 |  |
Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Discount rate | 3.35% | 4.30% |
Increase in pension benefit liability if there was a 50 basis point decrease in the weighted average discount rate | $ 42 |  |
Increase in benefits expense if there was a 50 basis point decrease in the weighted average discount rate | 4 |  |
Expected employer contributions to pension and postretirement plans | $ 47 |  |
Other Postretirement Benefits | Deposit Administration Fund |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Percent of plan assets invested | 100.00% |  |

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