Pension and Other Postretirement Plans (Defined Pension and Other Postretirement Plans) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Effect on post retirement benefit obligation, 1% Decrease		$ 181
Effect on total service and interest cost, 1% Decrease		11
Postretirement Medical Plan | Flight Attendant Postretirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain recognition of prior service credit		47
Postretirement Medical Plan | Technicians and Related Employees Postretirement Medical Plans
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain recognition of prior service credit		60
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain recognition of prior service credit		107
Effect on post retirement benefit obligation, 1% Decrease		149
Effect on total service and interest cost, 1% Decrease		11
Employer contributions		$ 119	$ 135
Other Postretirement Benefits | Deposit Administration Fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets		100.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 421	$ 824
United Airlines, Inc. | Other Postretirement Benefits | Scenario Forecast
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 108
United Airlines, Inc. | Pension Benefits | Scenario Forecast
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 400