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Details of Pass Through Trusts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Proceeds received from issuance of debt	$ 2,765	$ 808	$ 1,073
United Airlines, Inc.
Debt Instrument [Line Items]
Principal	497
Proceeds received from issuance of debt	2,765	$ 808	$ 1,073
United Airlines, Inc. | Class B Pass Through Certificates | November 2017
Debt Instrument [Line Items]
Principal	$ 258
Final expected distribution date	2026-01
Stated interest rate	3.65%
Total debt recorded	$ 258
Proceeds received from issuance of debt	258
United Airlines, Inc. | Class B Pass Through Certificates One | November 2017
Debt Instrument [Line Items]
Principal	$ 236
Final expected distribution date	2025-10
Stated interest rate	3.65%
Total debt recorded	$ 236
Proceeds received from issuance of debt	236
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%
Remaining proceeds from issuance of debt to be received in future periods	$ 677
United Airlines, Inc. | Class AA Pass Through Certificates | September 2016
Debt Instrument [Line Items]
Principal	$ 637
Final expected distribution date	2028-10
Stated interest rate	2.875%
Total debt recorded	$ 637
Proceeds received from issuance of debt	557
United Airlines, Inc. | Class AA Pass Through Certificates | June 2016
Debt Instrument [Line Items]
Principal	$ 729
Final expected distribution date	2028-07
Stated interest rate	3.10%
Total debt recorded	$ 729
Proceeds received from issuance of debt	319
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%
Remaining proceeds from issuance of debt to be received in future periods	$ 258
United Airlines, Inc. | Class A Pass Through Certificates | September 2016
Debt Instrument [Line Items]
Principal	$ 283
Final expected distribution date	2028-10
Stated interest rate	3.10%
Total debt recorded	$ 283
Proceeds received from issuance of debt	247
United Airlines, Inc. | Class A Pass Through Certificates | June 2016
Debt Instrument [Line Items]
Principal	$ 324
Final expected distribution date	2028-07
Stated interest rate	3.45%
Total debt recorded	$ 324
Proceeds received from issuance of debt	142
United Airlines, Inc. | EETC
Debt Instrument [Line Items]
Principal	3,402
Total debt recorded	2,467
Proceeds received from issuance of debt	1,759
Remaining proceeds from issuance of debt to be received in future periods	$ 935

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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