Fair value measurements, investments and notes receivable - Narrative (Details) $ in Millions	3 Months Ended
Mar. 31, 2024 USD ($) aircraft
Fair Value [Line Items]
Equity method investments	$ 230
Carrying amount of loan receivable	$ 86
Republic Airways Holdings Inc.
Fair Value [Line Items]
Number of aircraft operated \| aircraft	66
Champlain Enterprises LLC
Fair Value [Line Items]
Number of aircraft operated \| aircraft	53
Republic Airways Holdings Inc.
Fair Value [Line Items]
Ownership stake	19.00%
CommuteAir LLC
Fair Value [Line Items]
Ownership stake	40.00%
United Airlines Ventures Sustainable Flight Fund
Fair Value [Line Items]
Ownership stake	33.00%
Fulcrum BioEnergy, Inc., Boom, Alder Fuels LLC, Heart Aerospace Incorporated and ZeroAvia, Inc.
Fair Value [Line Items]
Investment carrying value	$ 421
Corporate Debt \| Maximum
Fair Value [Line Items]
Available-for-sale securities remaining maturities	17 months

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Fair Value [Line Items]

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
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-Publisher FASB
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481664/323-10-45-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 25
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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
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-Section 50
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- Definition

Amortized cost, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Number of aircraft operated by the carrier.

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