Income Tax Provision Differed from Amounts Computed at Statutory Federal Income Tax Rate (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Income tax provision at statutory rate					$ 395	$ 189	$ (253)
State income taxes, net of federal income tax					16	5	(15)
Foreign income taxes					2	3	7
Nondeductible employee meals					15	15	12
Nondeductible interest expense							19
State rate change						(33)
Valuation allowance					(441)	(219)	234
Other, net					9	8	(5)
Income tax expense (benefit)	(6)	(3)	(1)	(7)	(4)	(32)	(1)
United Airlines, Inc.
Income Taxes [Line Items]
Income tax provision at statutory rate					388	223	(230)
State income taxes, net of federal income tax					15	5	(7)
Foreign income taxes					2	3	7
Nondeductible employee meals					15	15	12
Nondeductible interest expense							19
Derivative market adjustment					(7)	(24)	(15)
State rate change						(33)
Valuation allowance					(426)	(229)	223
Other, net					9	23	(5)
Income tax expense (benefit)					$ (4)	$ (17)	$ 4