Valuation and Qualifying Accounts (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Valuation allowance for deferred tax assets
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 4,591		$ 5,388		$ 4,922
Additions Charged to Costs and Expenses	156		7		487
Deductions			888	[1]	21	[1]
Other	4	[2]	84	[2]
Balance at End of Period	4,751		4,591		5,388
UAL and United | Allowance for doubtful accounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	13		13		7
Additions Charged to Costs and Expenses	45		35		12
Deductions	36	[1]	35	[1]	6	[1]
Balance at End of Period	22		13		13
UAL and United | Obsolescence allowance-spare parts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	162		125		89
Additions Charged to Costs and Expenses	35		38		40
Deductions	28	[1]	1	[1]	4	[1]
Balance at End of Period	169		162		125
United Airlines, Inc. | Valuation allowance for deferred tax assets
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	4,561		5,288		4,833
Additions Charged to Costs and Expenses	167		8		661
Deductions			898	[1]	206	[1]
Other	(7)	[2]	163	[2]
Balance at End of Period	$ 4,721		$ 4,561		$ 5,288

[1] Deduction from reserve for purpose for which reserve was created.

[2] See Note 7 to the financial statements included in Part II, Item 8 of this report for additional information related to other valuation allowance adjustments.