Fair Value Measurements - Carrying Amounts and Estimated Fair Values of the Company’s Debt (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	$ 474	$ 431
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	465	412
Pre-delivery credit facility | Carrying Value | Secured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	312	277
Pre-delivery credit facility | Estimated Fair Value | Secured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	316	277
Floating rate building note | Carrying Value | Secured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	16	17
Floating rate building note | Estimated Fair Value | Secured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	16	17
Affinity card advance purchase of miles | Carrying Value | Unsecured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	80	71
Affinity card advance purchase of miles | Estimated Fair Value | Unsecured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	76	66
PSP Promissory Notes | Carrying Value | Unsecured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	66	66
PSP Promissory Notes | Estimated Fair Value | Unsecured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt, fair value	$ 57	$ 52