Common Stockholders' Equity and Preferred Securities - Additional Information (Detail) (USD $)	12 Months Ended		0 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2012	Jul. 24, 2014	Dec. 31, 2013	Jan. 31, 2014	Jan. 31, 2015	Jan. 31, 2015
Schedule Of Stockholders Equity [Line Items]
Debt purchased and retired		$ 212,000,000
Long-term Debt, Gross	248,000,000
Share repurchase program authorized amount			1,000,000,000
Number of accelerated shares repurchase programs			2
Agreement to repurchase through an accelerated share repurchase program			200,000,000
Payments for repurchases of common stock	312,000,000
Common stock reserved for future issuance	21,000,000
Junior preferred stock outstanding	2
Junior preferred stock par value per share	$ 0.01
Preferred stock authorized to issue	250,000,000
Accelerated Share Repurchase Program
Schedule Of Stockholders Equity [Line Items]
Payments for repurchases of common stock			200,000,000
Number of shares repurchased			4,400,000
Open Market Repurchases
Schedule Of Stockholders Equity [Line Items]
Payments for repurchases of common stock	120,000,000
Number of shares repurchased	2,100,000
6% Convertible Senior Notes
Schedule Of Stockholders Equity [Line Items]
Debt instrument stated interest rate	6.00%			6.00%
Common stock issued in exchange for conversion notes	12,000,000			28,000,000
Debt instrument maturity year	2029			2029
Debt instrument converted amount	104,000,000
4.5% Convertible Notes Due 2015
Schedule Of Stockholders Equity [Line Items]
Debt instrument stated interest rate	4.50%
United Airlines, Inc.
Schedule Of Stockholders Equity [Line Items]
Long-term Debt, Gross	11,533,000,000			11,604,000,000
Dividend paid	212,000,000
Receivable from related parties	5,000,000			232,000,000
Number of affiliates				2
Unsecured Debt
Schedule Of Stockholders Equity [Line Items]
Debt instrument stated interest rate					4.50%
Common stock issued in exchange for conversion notes					5,000,000
Debt instrument maturity year					2021
Debt instrument converted amount					156,000,000
Unsecured Debt | 4.5% Convertible Notes Due 2015
Schedule Of Stockholders Equity [Line Items]
Debt purchased and retired	28,000,000
Debt instrument conversion rate	18.93
Payment to extinguish debt	62,000,000
Debt instrument stated interest rate	4.50%
Long-term Debt, Gross	202,000,000
Adjustment to additional paid in capital upon debt redemption	34,000,000
Debt instrument maturity year	2015
Unsecured Debt | 4.5% Convertible Notes Due 2015 | Subsequent Event
Schedule Of Stockholders Equity [Line Items]
Debt instrument stated interest rate						4.50%	4.50%
Long-term Debt, Gross						202,000,000	202,000,000
Common stock issued in exchange for conversion notes							11,000,000
Debt instrument converted amount						202,000,000
Unsecured Debt | United Airlines, Inc. | 4.5% Convertible Notes Due 2015
Schedule Of Stockholders Equity [Line Items]
Debt instrument stated interest rate	4.50%			4.50%
Long-term Debt, Gross	202,000,000			230,000,000
Adjustment to additional paid in capital upon debt redemption	$ 62,000,000
Debt instrument maturity year	2015			2015