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%