Debt - Narrative (Details) - USD ($)		6 Months Ended
Apr. 21, 2021	Jun. 30, 2021
Debt Instrument [Line Items]
Unamortized debt discount		$ 600,000,000
Term Loan Facility \| Secured Debt
Debt Instrument [Line Items]
Face amount	$ 1,400,000,000	1,400,000,000
PSP2 Note \| Unsecured Debt
Debt Instrument [Line Items]
Face amount		$ 870,000,000
Term of debt		10 years
PSP2 Note \| Years 1 through 5 \| Unsecured Debt
Debt Instrument [Line Items]
Stated interest rate		1.00%
PSP2 Note \| Years 6 through 10 \| Unsecured Debt \| SOFR
Debt Instrument [Line Items]
Percent spread on variable rate		2.00%
PSP3 Note \| Unsecured Debt
Debt Instrument [Line Items]
Face amount		$ 810,000,000
Term of debt		10 years
PSP3 Note \| Years 1 through 5 \| Unsecured Debt
Debt Instrument [Line Items]
Stated interest rate		1.00%
PSP3 Note \| Years 6 through 10 \| Unsecured Debt \| SOFR
Debt Instrument [Line Items]
Percent spread on variable rate		2.00%
2026 Notes and 2029 Notes \| Secured Debt
Debt Instrument [Line Items]
Face amount	4,000,000,000.0	$ 4,000,000,000.0
2026 Notes \| Secured Debt
Debt Instrument [Line Items]
Face amount	$ 2,000,000,000.0	$ 2,000,000,000.0
Stated interest rate	4.375%	4.375%
Issuance price as a percent of principal amount	100.00%
2029 Notes \| Secured Debt
Debt Instrument [Line Items]
Face amount	$ 2,000,000,000.0	$ 2,000,000,000.0
Stated interest rate	4.625%	4.625%
Issuance price as a percent of principal amount	100.00%
Term Loan B Facility due 2028 \| Secured Debt
Debt Instrument [Line Items]
Face amount	$ 5,000,000,000.0	$ 5,000,000,000.0
Quarterly installment repayment as a percent of the original principal amount	0.25%
Term Loan B Facility due 2028 \| Secured Debt \| LIBOR
Debt Instrument [Line Items]
Percent spread on variable rate	3.75%
Interest rate floor	0.75%
CARES Act Term Loan Facility \| Secured Debt
Debt Instrument [Line Items]
Face amount	$ 520,000,000	520,000,000
Revolving Credit Facility \| Senior Secured Revolving Credit Facility due 2025 \| Secured Debt
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,750,000,000	1,750,000,000
Commitment fee percentage	0.75%
Revolving Credit Facility \| Senior Secured Revolving Credit Facility due 2025 \| Secured Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Percent spread on variable rate	3.00%
Revolving Credit Facility \| Senior Secured Revolving Credit Facility due 2025 \| Secured Debt \| LIBOR \| Maximum
Debt Instrument [Line Items]
Percent spread on variable rate	3.50%
Revolving Credit Facility \| Credit Agreement \| Secured Debt
Debt Instrument [Line Items]
Face amount	$ 1,000,000,000.0	1,000,000,000.0
Revolving Credit Facility \| United Airlines, Inc. \| Secured Debt
Debt Instrument [Line Items]
Available under revolving credit facility		$ 1,750,000,000

Debt Instrument, Issuance Price, Percentage

No definition available.

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- Definition

Debt Instrument, Quarterly Installment Percentage

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Variable Rate Floor

+ References

No definition available.

+ Details

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

Amount, after accumulated amortization, of debt discount.

+ References

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+ Details

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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-Publisher FASB
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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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