Components of Accumulated Other Comprehensive Income (loss), Net of Tax (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 United Airlines, Inc.	Mar. 31, 2012 United Airlines, Inc.	Mar. 31, 2013 Accumulated Defined Benefit Plans Adjustment	Mar. 31, 2012 Accumulated Defined Benefit Plans Adjustment	Mar. 31, 2013 Accumulated Defined Benefit Plans Adjustment United Airlines, Inc.	Mar. 31, 2012 Accumulated Defined Benefit Plans Adjustment United Airlines, Inc.	Mar. 31, 2013 Accumulated Net Unrealized Investment Gain (Loss)	Mar. 31, 2012 Accumulated Net Unrealized Investment Gain (Loss)	Mar. 31, 2013 Accumulated Net Unrealized Investment Gain (Loss) United Airlines, Inc.	Mar. 31, 2012 Accumulated Net Unrealized Investment Gain (Loss) United Airlines, Inc.	Mar. 31, 2013 Other Accumulated Other Comprehensive Income	Mar. 31, 2012 Other Accumulated Other Comprehensive Income	Mar. 31, 2013 Other Accumulated Other Comprehensive Income United Airlines, Inc.	Mar. 31, 2012 Other Accumulated Other Comprehensive Income United Airlines, Inc.	Mar. 31, 2013 Income Tax Benefit Expense United Airlines, Inc.	Mar. 31, 2012 Income Tax Benefit Expense United Airlines, Inc.	Dec. 31, 2011 Income Tax Benefit Expense United Airlines, Inc.
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	$ (1,046)	$ (417)	$ (1,053)	$ (425)	$ (1,042)	$ (312)	$ (1,042)	$ (312)	$ (10)	$ (99)	$ (10)	$ (99)	$ 6	$ (6)	$ 5	$ (8)	$ (6)	$ (6)	$ (6)
Other comprehensive income before reclassifications	(11)	102	(10)	103					(9)	93	(9)	93	(2)	9	(1)	10
Amounts reclassified from accumulated other comprehensive income	30	35	36	35	21	4	21	4	9	31	9	31					6
Net current-period other comprehensive income	19	137	26	138	21	4	21	4		124		124	(2)	9	(1)	10	6
Ending Balance	$ (1,027)	$ (280)	$ (1,027)	$ (287)	$ (1,021)	$ (308)	$ (1,021)	$ (308)	$ (10)	$ 25	$ (10)	$ 25	$ 4	$ 3	$ 4	$ 2		$ (6)	$ (6)