Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation allowance for deferred tax assets
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 48	$ 4,751	$ 4,591
Additions Charged to Costs and Expenses		47		156
Deductions	[1]	27	4,703
Other				4
Balance at End of Period		68	48	4,751
UAL and United | Allowance for doubtful accounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		18	22	13
Additions Charged to Costs and Expenses		18	25	45
Deductions	[1]	26	29	36
Balance at End of Period		10	18	22
UAL and United | Obsolescence allowance-spare parts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		235	169	162
Additions Charged to Costs and Expenses		61	38	35
Deductions	[1]	16		28
Other		15	28
Balance at End of Period		295	235	169
United Airlines, Inc. | Valuation allowance for deferred tax assets
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		48	4,721	4,561
Additions Charged to Costs and Expenses		47		167
Deductions	[1]	27	4,673
Other				(7)
Balance at End of Period		$ 68	$ 48	$ 4,721

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