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Special Charges - Additional Information (Detail) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) Technician | Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) VEF / $ | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) Contract plan | Dec. 31, 2015 USD ($) VEF / $ | Dec. 31, 2014 USD ($) Attendant
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Severance and benefits costs | $ 15,000,000 | $ 23,000,000 | $ 41,000,000 | $ 37,000,000 | $ 10,000,000 | $ 13,000,000 | $ 6,000,000 | $ 8,000,000 |  | $ 116,000,000 | $ 37,000,000 | $ 107,000,000 |
Severance and benefits costs net of tax |  |  |  |  |  |  |  |  |  |  | 24,000,000 |  |
Impairment of assets | $ 10,000,000 | $ 15,000,000 |  |  |  |  | 412,000,000 |  |  | 25,000,000 | $ 412,000,000 | 79,000,000 |
Impairment of indefinite-lived intangible assets |  |  |  |  |  |  |  |  | $ 33,000,000 |  |  |  |
Impairment of indefinite-lived intangible assets, net of tax benefits |  |  |  |  |  |  |  |  | 22,000,000 |  |  |  |
Lease maturity year |  |  |  |  |  |  |  |  |  |  | 2029 |  |
Cleveland airport lease restructuring |  |  |  |  |  |  |  | 74,000,000 |  |  | $ 74,000,000 |  |
Cleveland airport lease restructuring, net of taxes |  |  |  |  |  |  |  |  |  |  | 47,000,000 |  |
Labor agreement costs |  |  |  |  | $ (60,000,000) | $ 14,000,000 | 10,000,000 | 100,000,000 |  |  | 64,000,000 | 18,000,000 |
Costs associated with aircraft |  |  |  |  |  |  |  |  | 8,000,000 |  |  |  |
Inventory held for sale |  |  |  |  |  |  |  |  | $ 7,000,000 |  |  | 7,000,000 |
Impairment for discontinued internal software projects |  |  |  |  |  |  |  |  |  |  |  | 10,000,000 |
Impairment of assets held for disposal |  |  |  |  |  |  |  |  |  |  |  | 10,000,000 |
Collective bargaining agreements |  |  |  |  |  |  |  |  |  |  |  | 18,000,000 |
Integration-related costs |  |  |  |  |  |  |  |  |  |  |  | 60,000,000 |
Charges for legal matters |  |  |  |  |  |  |  |  |  |  |  | 32,000,000 |
Cease use of an aircraft under lease |  |  |  |  |  |  |  |  |  |  |  | 16,000,000 |
Losses (gain) on extinguishment of debt and other |  |  |  |  |  |  | $ (9,000,000) | $ 8,000,000 |  |  | $ (1,000,000) | 202,000,000 |
Venezuela local currency loss |  |  |  |  |  |  |  |  |  |  |  | $ 61,000,000 |
Foreign currency exchange rate | VEF / $ |  |  |  |  |  |  |  |  | 200 |  |  | 200 |
Foreign currency exchange rate per US dollar, description |  |  |  |  |  |  |  |  |  |  |  | 200 Venezuelan bolivars to one U.S. dollar |
Venezuelan bolivars |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Unrestricted cash balance held as Venezuelan bolivars |  |  |  |  |  |  |  |  | $ 13,000,000 |  |  | $ 13,000,000 |
Postretirement Medical Plan | Flight Attendant Postretirement Medical Plan |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of plans amended | plan |  |  |  |  |  |  |  |  |  |  | 2 |  |
Curtailment gain recognition of prior service credit |  |  |  |  |  |  |  |  |  |  | $ 47,000,000 |  |
Curtailment gain recognition of prior service credit,net of tax |  |  |  |  |  |  |  |  |  |  | 30,000,000 |  |
Newark Liberty International Airport |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of indefinite-lived intangible assets |  |  |  |  |  |  |  |  |  |  | 412,000,000 |  |
Impairment of indefinite-lived intangible assets, net of tax benefits |  |  |  |  |  |  |  |  |  |  | 264,000,000 |  |
United Airlines, Inc. | 6% Notes due 2026 and 2028 |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Write off of unamortized discount |  |  |  |  |  |  |  |  |  |  |  | $ 134,000,000 |
Scenario, Previously Reported |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Foreign currency exchange rate | VEF / $ |  |  |  |  |  |  |  |  | 13.5 |  |  | 13.5 |
Foreign currency exchange rate per US dollar, description |  |  |  |  |  |  |  |  |  |  |  | 13.5 Venezuelan bolivars to one U.S. dollar |
International Brotherhood of Teamsters |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Severance and benefits costs |  |  |  |  |  |  |  |  |  | 83,000,000 |  |  |
Severance and benefits costs net of tax |  |  |  |  |  |  |  |  |  | 53,000,000 |  |  |
Int'l Association of Machinists |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Curtailment gain recognition of prior service credit |  |  |  |  |  |  |  |  |  |  | 60,000,000 |  |
Curtailment gain recognition of prior service credit,net of tax |  |  |  |  |  |  |  |  |  |  | $ 38,000,000 |  |
Number of new contracts extended | Contract |  |  |  |  |  |  |  |  |  |  | 7 |  |
Service contract extended year |  |  |  |  |  |  |  |  |  |  | 2021 |  |
Labor agreement costs |  |  |  |  |  |  |  |  |  |  | $ 171,000,000 |  |
Labor agreement costs net of tax |  |  |  |  |  |  |  |  |  |  | $ 110,000,000 |  |
Voluntary early out program |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of positions eliminated | Attendant |  |  |  |  |  |  |  |  |  |  |  |  | 2,500
Voluntary early out program | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Severance payment per participant |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000
Voluntary early out program | International Brotherhood of Teamsters |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of positions eliminated | Technician |  |  |  | 1,000 |  |  |  |  |  |  |  |  |
Voluntary early out program | International Brotherhood of Teamsters | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Severance payment per participant |  |  |  | $ 100,000 |  |  |  |  |  |  |  |  |
Management Reorganization Initiative |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Severance and benefits costs |  |  |  |  |  |  |  |  |  | 33,000,000 |  |  |
Severance and benefits costs net of tax |  |  |  |  |  |  |  |  |  | 21,000,000 |  |  |
Integration Related |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
(Gains) losses on sale of assets and other miscellaneous (gains) losses, net |  |  |  |  |  |  |  |  |  |  |  | $ 14,000,000 |
Obsolete Spare Parts Inventory |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  |  |  |  | 10,000,000 |  |  |
Impairment of assets net of tax |  |  |  |  |  |  |  |  |  | 6,000,000 |  |  |
Maintenance Service Agreement |  |  |  |  |  |  |  |  |  |  |  |  |
Special Charges [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  |  |  |  | 15,000,000 |  |  |
Impairment of assets net of tax |  |  |  |  |  |  |  |  |  | $ 10,000,000 |  |  |

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