Debt - Details of Pass Through Trusts (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Debt Instrument [Line Items]
Total proceeds received from issuance of debt during 2018 and recorded as debt as of June 30, 2018	$ 1,308	$ 1,139
United Airlines, Inc.
Debt Instrument [Line Items]
Principal	1,161
Total proceeds received from issuance of debt during 2018 and recorded as debt as of June 30, 2018	1,308	$ 1,139
United Airlines, Inc. \| Class AA Pass Through Certificates \| February 2018
Debt Instrument [Line Items]
Principal	$ 677
Stated interest rate	3.50%
Total proceeds received from issuance of debt during 2018 and recorded as debt as of June 30, 2018	$ 677
United Airlines, Inc. \| Class A Pass Through Certificates \| February 2018
Debt Instrument [Line Items]
Principal	$ 258
Stated interest rate	3.70%
Total proceeds received from issuance of debt during 2018 and recorded as debt as of June 30, 2018	$ 258
United Airlines, Inc. \| Class B Pass Through Certificates \| May 2018
Debt Instrument [Line Items]
Principal	$ 226
Stated interest rate	4.60%
Total proceeds received from issuance of debt during 2018 and recorded as debt as of June 30, 2018	$ 226
United Airlines, Inc. \| Pass Through Certificates
Debt Instrument [Line Items]
Total proceeds received from issuance of debt during 2018 and recorded as debt as of June 30, 2018	$ 1,161

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

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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+ 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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+ References

No definition available.

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+ 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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