Financial Instruments and Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended
Mar. 31, 2023 USD ($) aircraft
Fair Value [Line Items]
Equity method investments	$ 208
CommuteAir LLC
Fair Value [Line Items]
Ownership stake	40.00%
Number of aircraft operated \| aircraft	61
Republic Airways Holdings Inc.
Fair Value [Line Items]
Ownership stake	19.00%
Number of aircraft operated \| aircraft	66
United Airlines Ventures Sustainable Flight Fund
Fair Value [Line Items]
Ownership stake	49.99%
Initial commitment	$ 100
Blue Blade Energy, LLC
Fair Value [Line Items]
Ownership stake	20.00%
Fulcrum BioEnergy, Inc., Boom, Alder Fuels LLC, Heart Aerospace Incorporated and ZeroAvia, Inc.
Fair Value [Line Items]
Investment carrying value	$ 413
Corporate Debt \| Maximum
Fair Value [Line Items]
Available-for-sale securities remaining maturities	2 years

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Fair Value [Line Items]

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Initial Commitments from Company and Other Corporate Investors, Amount

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of investment in equity security without readily determinable fair value.

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Number of aircraft operated by the carrier.

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