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Fair Value of Financial Instruments - Significant Unobservable Inputs (Details) - Fair Value, Recurring - Level 3
$ in Millions
Dec. 31, 2024
USD ($)
$ / MWh
$ / BTU
MWh
Dec. 31, 2023
USD ($)
MWh
$ / MWh
$ / BTU
Low | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / BTU 0.85 1.25
High | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / BTU 10.55 13.69
Weighted Average | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / BTU 3.25 4.93
Long-term Power Commodity Contracts | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset | $ $ 0 $ 0
Derivative liability | $ $ 366 $ 325
Long-term Power Commodity Contracts | Low | Measurement Input, Commodity Forward Price | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / MWh 21.60 18.18
Long-term Power Commodity Contracts | High | Measurement Input, Commodity Forward Price | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / MWh 80.82 81.62
Long-term Power Commodity Contracts | Weighted Average | Measurement Input, Commodity Forward Price | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / MWh 45.44 39.91
Commodity Contracts | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset | $ $ 9 $ 0
Derivative liability | $ $ 5 $ 5
Commodity Contracts | Low | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / MWh (19.30) (43.96)
Commodity Contracts | High | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / MWh 1,011.79 343.61
Commodity Contracts | Weighted Average | Measurement Input, Commodity Forward Price | Valuation Technique, Option Model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | $ / MWh 45.87 64.34
Other Financial Instruments | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset | $ $ 10 $ 13
Derivative liability | $ $ 0 $ 0
Other Financial Instruments | Low | Measurement Input, Commodity Forward Price | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | MWh 59,425 60,801
Other Financial Instruments | High | Measurement Input, Commodity Forward Price | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | MWh 118,850 121,602
Other Financial Instruments | Weighted Average | Measurement Input, Commodity Forward Price | Valuation Technique, Discounted Cash Flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Derivative asset/liability measurement input (in dollars per megawatt-hour or British thermal unit) | MWh 111,091 115,622