Income Tax Provision Differed from Amounts Computed at Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Income tax provision at statutory rate				$ 1,337	$ 1,477	$ 395
State income taxes, net of federal income tax				38	38	10
Foreign income taxes				3	4	2
Nondeductible employee meals				16	15	15
Income tax adjustment	$ 180	$ 88	$ (3,218)	180	(3,130)
State rate change				(12)
Valuation allowance				20	(4,662)	(435)
Other, net				(26)	7	9
Income tax expense (benefit)				1,556	(3,121)	(4)
United Airlines, Inc.
Income Taxes [Line Items]
Income tax provision at statutory rate				1,338	1,477	388
State income taxes, net of federal income tax				38	38	10
Foreign income taxes				3	4	2
Nondeductible employee meals				16	15	15
Derivative market adjustment						(7)
Income tax adjustment				180
State rate change				(12)
Valuation allowance				20	(4,621)	(421)
Other, net				(25)	7	9
Income tax expense (benefit)				$ 1,558	$ (3,080)	$ (4)