Common Stockholders' Equity and Preferred Securities - Summary of Warrants Outstanding (Details) shares in Millions	Dec. 31, 2023 $ / shares shares
Class of Warrant or Right [Line Items]
Number of Shares of UAL Common Stock (in shares)	10.0
PSP1 Warrants
Class of Warrant or Right [Line Items]
Number of Shares of UAL Common Stock (in shares)	4.8
Exercise Price (in dollars per share) | $ / shares	$ 31.50
CARES Act Warrants
Class of Warrant or Right [Line Items]
Number of Shares of UAL Common Stock (in shares)	1.7
Exercise Price (in dollars per share) | $ / shares	$ 31.50
PSP2 Warrants
Class of Warrant or Right [Line Items]
Number of Shares of UAL Common Stock (in shares)	2.0
Exercise Price (in dollars per share) | $ / shares	$ 43.26
PSP3 Warrants
Class of Warrant or Right [Line Items]
Number of Shares of UAL Common Stock (in shares)	1.5
Exercise Price (in dollars per share) | $ / shares	$ 53.92