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Pension and Other Postretirement Plans (Defined Pension and Other Postretirement Plans) - Additional Information (Detail) - 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   $ 185  
Effect on benefit expense, 1% Decrease   8  
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Employer contributions   $ 108 $ 119
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   $ 419 $ 421
United Airlines, Inc. | Other Postretirement Benefits | Scenario Forecast      
Defined Benefit Plan Disclosure [Line Items]      
Employer contributions $ 109    
United Airlines, Inc. | Pension Benefits | Scenario Forecast      
Defined Benefit Plan Disclosure [Line Items]      
Employer contributions $ 420