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Financial Instruments - Narrative (Details)
3 Months Ended
Dec. 31, 2024
USD ($)
MMcf
Dec. 31, 2023
USD ($)
Sep. 30, 2024
USD ($)
Derivative [Line Items]      
Purchase commitment volume | MMcf 15,053    
Contract netting $ 0   $ 0
Cash collateral 0   $ 0
Net (gain) loss on settled interest rate agreements (5,100,000) $ (3,200,000)  
Net realized gains in AOCI $ 391,000,000.0    
Designated As Hedge | Gas Purchases | Commodity contracts      
Derivative [Line Items]      
Purchase commitment volume | MMcf 24,000.0    
Designated As Hedge | Gas Purchases | Commodity contracts | Minimum      
Derivative [Line Items]      
Hedging percent 25.00%    
Designated As Hedge | Gas Purchases | Commodity contracts | Maximum      
Derivative [Line Items]      
Hedging percent 50.00%