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Fair Value Measurements and Derivative Instruments - Schedule of Fuel Price Risk (Details) - Fuel Swap Agreements
$ in Millions
Jun. 30, 2024
USD ($)
T
Dec. 31, 2023
USD ($)
T
Derivative Instruments    
Estimated unrealized net gain (loss) associated with cash flow hedges pertaining to fuel swap agreements expected to be reclassified to earnings from accumulated other comprehensive income loss | $ $ 36 $ (21)
2024    
Derivative Instruments    
Fuel Swap Agreements (metric tons) 524,701 1,054,501
Percentage of projected requirements 61.00% 61.00%
2025    
Derivative Instruments    
Fuel Swap Agreements (metric tons) 773,700 685,400
Percentage of projected requirements 45.00% 39.00%
2026    
Derivative Instruments    
Fuel Swap Agreements (metric tons) 430,350 44,200
Percentage of projected requirements 24.00% 3.00%