Pension and Other Postretirement Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Effect on post retirement benefit obligation, 1% Decrease	$ 139
Effect on total service and interest cost, 1% Decrease	10
Profit sharing and payroll tax expense	$ 334	$ 349	$ 628
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 | Multi-Employer Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Multi-employer plan contributions		$ 435
IAM National Pension Plan | Multi-Employer Pension Plans | Minimum
Defined Benefit Plan Disclosure [Line Items]
Percent of company's contribution to plan		5.00%
United Airlines, Inc.
Defined Benefit Plan Disclosure [Line Items]
Expense for defined contribution plans	$ 693	$ 656	$ 592
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%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions to pension and postretirement plans	$ 318
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions to pension and postretirement plans	$ 95
Other Postretirement Benefits | Deposit Administration Fund
Defined Benefit Plan Disclosure [Line Items]
Percent of plan assets invested	100.00%