v3.26.3
Fair Value of Financial Instruments - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details) - Level 3
$ in Millions
Sep. 30, 2026
USD ($)
$ / MWh
MWh
$ / BTU
Low | Forward Market Price | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / BTU 1.02
High | Forward Market Price | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / BTU 12.54
Weighted Average | Forward Market Price | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / BTU 3.61
Long-term Power Commodity Contracts | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Assets | $ $ 0
Liabilities | $ $ 69
Long-term Power Commodity Contracts | Low | Forward Market Price | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / MWh 30.29
Long-term Power Commodity Contracts | High | Forward Market Price | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / MWh 77.57
Long-term Power Commodity Contracts | Weighted Average | Forward Market Price | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / MWh 46.43
Heat Rate Call Option Commodity Contracts | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Assets | $ $ 14
Liabilities | $ $ 3
Heat Rate Call Option Commodity Contracts | Low | Forward Market Price | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / MWh (24.36)
Heat Rate Call Option Commodity Contracts | High | Forward Market Price | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / MWh 286.87
Heat Rate Call Option Commodity Contracts | Weighted Average | Forward Market Price | Option Model  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | $ / MWh 49.72
Other Financial Instruments | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Assets | $ $ 4
Liabilities | $ $ 0
Other Financial Instruments | Low | Forward Market Price | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | MWh 57,935
Other Financial Instruments | High | Forward Market Price | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | MWh 115,869
Other Financial Instruments | Weighted Average | Forward Market Price | Discounted Cash Flow  
Fair Value Measurement Inputs and Valuation Techniques [Line Items]  
Input/Range | MWh 97,214