Details of Pass Through Trusts (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Debt Instrument [Line Items]
Total proceeds received from issuance of debt during 2018 and recorded as debt	$ 696	$ 755
United Airlines, Inc.
Debt Instrument [Line Items]
Principal	935
Total proceeds received from issuance of debt during 2018 and recorded as debt	696	$ 755
United Airlines, Inc. \| February Twenty Eighteen [Member]
Debt Instrument [Line Items]
Total proceeds received from issuance of debt during 2018 and recorded as debt	657
Remaining proceeds from issuance of debt to be received in future periods	278
United Airlines, Inc. \| Class AA Pass Through Certificates \| February Twenty Eighteen [Member]
Debt Instrument [Line Items]
Principal	$ 677
Final expected distribution date	2030-03
Stated interest rate	3.50%
Total proceeds received from issuance of debt during 2018 and recorded as debt	$ 476
Remaining proceeds from issuance of debt to be received in future periods	201
United Airlines, Inc. \| Class A Pass Through Certificates \| February Twenty Eighteen [Member]
Debt Instrument [Line Items]
Principal	$ 258
Final expected distribution date	2030-03
Stated interest rate	3.70%
Total proceeds received from issuance of debt during 2018 and recorded as debt	$ 181
Remaining proceeds from issuance of debt to be received in future periods	$ 77

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- Definition

Amount of borrowing capacity currently available under the debt instrument (initial borrowing capacity less the amount of proceeds received).

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

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- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

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