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Fair Value Measurements and Derivative Instruments - Schedule of Outstanding Fuel Swap Agreements (Details) - Fuel Price Risk
$ in Millions
Dec. 31, 2024
USD ($)
T
Dec. 31, 2023
USD ($)
T
Derivative instruments disclosure    
Estimated unrealized net gains (losses) associated with cash flow hedges pertaining to fuel swap agreements expected to be reclassified to earnings from other accumulated comprehensive income (loss) | $ $ (9) $ (21)
2025    
Derivative instruments disclosure    
Fuel swap agreements (metric tons) 1,031,449,000 685,400,000
Percentage of projected requirements 60.00% 39.00%
2026    
Derivative instruments disclosure    
Fuel swap agreements (metric tons) 786,750,000 44,200,000
Percentage of projected requirements 44.00% 3.00%
2027    
Derivative instruments disclosure    
Fuel swap agreements (metric tons) 364,048,000 0
Percentage of projected requirements 20.00% 0.00%