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Leases and Capacity Purchase Agreements - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Aircraft
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Capital Leased Assets [Line Items]        
Regional capacity purchase expense   $ 2,232,000,000 $ 2,197,000,000 $ 2,290,000,000
Expenses   34,238,000,000 32,218,000,000 32,698,000,000
Accounts payable   2,196,000,000 2,139,000,000  
Capacity Purchase Agreements | Scenario Forecast        
Capital Leased Assets [Line Items]        
Scheduled block hours increase (decrease) percentage 10.00%      
Change in cash obligation $ 147,000,000      
Aircraft Operating Leases        
Capital Leased Assets [Line Items]        
Operating leases obligations   $ 4,932,000,000    
Minimum | Aircraft Operating Leases        
Capital Leased Assets [Line Items]        
Operating lease term   5 years    
Operating lease expiration date, in years   2018    
Maximum | Aircraft Operating Leases        
Capital Leased Assets [Line Items]        
Operating lease term   26 years    
Operating lease expiration date, in years   2029    
United Airlines, Inc.        
Capital Leased Assets [Line Items]        
Nonaircraft rent expense   $ 1,300,000,000 1,200,000,000 1,300,000,000
Regional capacity purchase expense   $ 2,232,000,000 2,197,000,000 2,290,000,000
Number of aircrafts under the extended term of contract | Aircraft   125    
Capacity purchase agreement contract expiration date after extension   Dec. 31, 2022    
Expenses   $ 34,236,000,000 32,215,000,000 32,696,000,000
Accounts payable   $ 2,196,000,000 2,144,000,000  
United Airlines, Inc. | Capacity Purchase Agreements        
Capital Leased Assets [Line Items]        
Number of regional aircraft | Aircraft   518    
Airline capacity purchase arrangements, expiration year   2029    
United Airlines, Inc. | Revaluation of Liabilities        
Capital Leased Assets [Line Items]        
Net accretion amounts   $ 79,000,000 82,000,000 107,000,000
United Airlines, Inc. | Regional Aircraft        
Capital Leased Assets [Line Items]        
Regional capacity purchase expense   458,000,000 439,000,000 461,000,000
United Airlines, Inc. | Variable Interest Entity, Not Primary Beneficiary        
Capital Leased Assets [Line Items]        
Operating leases obligations   $ 1,400,000,000    
United Airlines, Inc. | Minimum        
Capital Leased Assets [Line Items]        
Imputed interest rate   3.50%    
Lease Fair Value Adjustment, Remaining Lease Term   1 year    
United Airlines, Inc. | Maximum        
Capital Leased Assets [Line Items]        
Imputed interest rate   20.80%    
Lease Fair Value Adjustment, Remaining Lease Term   7 years    
United Airlines, Inc. | Maximum | CRJ 200        
Capital Leased Assets [Line Items]        
Number of aircraft to operate | Aircraft   65    
United Airlines, Inc. | Mainline        
Capital Leased Assets [Line Items]        
Number of assets subject to lease | Aircraft   31    
United Airlines, Inc. | Regional Carrier        
Capital Leased Assets [Line Items]        
Number of assets subject to lease | Aircraft   43    
United Airlines, Inc. | Regional Carrier | Capacity Purchase Agreements        
Capital Leased Assets [Line Items]        
Expenses   $ 538,000,000 486,000,000 $ 366,000,000
Accounts payable   24,000,000 32,000,000  
Accounts receivable from regional carriers   $ 0 $ 0