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Pension and Other Postretirement Plans - Participation in the IAM National Pension Plan (Details) - IAM National Pension Plan - Pension Benefits - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Jan. 01, 2020
Multiemployer Plans [Line Items]        
Plan length 10 years      
Additional contribution as a percentage of the hourly contribution rate 0.025%      
Surcharge imposed No      
United Airlines, Inc.        
Multiemployer Plans [Line Items]        
Funded percentage       85.10%
Contributions $ 58 $ 53 $ 59