| Cover | Feb. 01, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 1, 2021 |
| Entity File Number | 001-10323 |
| Entity Registrant Name | UNITED AIRLINES, INC. |
| Entity Central Index Key | 0000319687 |
| Entity Tax Identification Number | 74-2099724 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 233 S. Wacker Drive |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60606 |
| City Area Code | 872 |
| Local Phone Number | 825-4000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
