Components of Accumulated Other Comprehensive Income (Loss), Net of Tax (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Increase in prior service credits	$ 3,000,000	$ 331,000,000
Increase in actuarial gains (losses)	(1,100,000,000)	1,300,000,000
United Airlines, Inc.
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (expense) benefit		6,000,000
Additional (losses) gains related to investments and other		$ 1,000,000	$ 1,000,000