Summary of Collateral Covenants and Cross Default Provisions (Detail)	12 Months Ended
	Dec. 31, 2017
Credit Agreement
Debt Instrument [Line Items]
Collateral, Covenants and Cross Default Provisions	Secured by certain of United’s international route authorities, specified take-off and landing slots at certain airports and certain other assets. The 2017 Credit Agreement requires the Company to maintain at least $2.0 billion of unrestricted liquidity at all times, which includes unrestricted cash, short-term investments and any undrawn amounts under any revolving credit facility, and to maintain a minimum ratio of appraised value of collateral to the outstanding obligations under the 2017 Credit Agreement of 1.6 to 1.0 at all times. The 2017 Credit Agreement contains covenants that, among other things, restrict the ability of UAL and its restricted subsidiaries (as defined in the 2017 Credit Agreement) to incur additional indebtedness and to pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company’s share repurchase program. The 2017 Credit Agreement contains events of default customary for this type of financing, including a cross default and cross acceleration provision to certain other material indebtedness of the Company.
6.375% Senior Notes due 2018
Debt Instrument [Line Items]
Collateral, Covenants and Cross Default Provisions	The indentures for these notes contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries (as defined in the indentures) to incur additional indebtedness and pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company’s share repurchase program.
6% Senior Notes due 2020
Debt Instrument [Line Items]
Collateral, Covenants and Cross Default Provisions	The indentures for these notes contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries (as defined in the indentures) to incur additional indebtedness and pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company’s share repurchase program.
5% Senior Notes due 2024
Debt Instrument [Line Items]
Collateral, Covenants and Cross Default Provisions	The indentures for these notes contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries (as defined in the indentures) to incur additional indebtedness and pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company’s share repurchase program.
4.25% Senior Notes due 2022
Debt Instrument [Line Items]
Collateral, Covenants and Cross Default Provisions	The indentures for these notes contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries (as defined in the indentures) to incur additional indebtedness and pay dividends on or repurchase stock, although the Company currently has ample ability under these restrictions to repurchase stock under the Company’s share repurchase program.