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Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) - Fuel derivative contracts - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Other Nonoperating Income (Expense) Other Nonoperating Income (Expense)
Cash Flow Hedging    
Derivative Instruments, Gain (Loss) [Line Items]    
(Gain) loss recognized in AOCI on derivatives, net of tax $ 29 $ (1)
Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
(Gain) loss recognized in income on derivatives $ 0 $ 1