v3.26.1
Fair Value Measurements - Schedule of Fair Value of the Level 3 Assets and Liabilities by Major Contract Type and the Significant Unobservable Inputs Used in the Valuations (Details) - Level 3
Jun. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Assets $ 366,000,000 $ 573,000,000
Liabilities (1,589,000,000) (1,842,000,000)
Total (1,223,000,000) (1,269,000,000)
Electricity purchases and sales | Income Approach    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Assets 132,000,000 269,000,000
Liabilities (1,411,000,000) (1,607,000,000)
Total (1,279,000,000) (1,338,000,000)
Electricity purchases and sales | Minimum | Income Approach | Hourly price curve shape    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 0 0
Electricity purchases and sales | Minimum | Income Approach | Illiquid delivery periods for hub power prices    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 30 25
Electricity purchases and sales | Minimum | Income Approach | Market Heat Rates    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 35 25
Electricity purchases and sales | Maximum | Income Approach | Hourly price curve shape    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 90 95
Electricity purchases and sales | Maximum | Income Approach | Illiquid delivery periods for hub power prices    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 145 135
Electricity purchases and sales | Maximum | Income Approach | Market Heat Rates    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 90 130
Electricity purchases and sales | Arithmetic Average | Income Approach | Hourly price curve shape    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 45 48
Electricity purchases and sales | Arithmetic Average | Income Approach | Illiquid delivery periods for hub power prices    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 88 80
Electricity purchases and sales | Arithmetic Average | Income Approach | Market Heat Rates    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 63 78
Options | Option Pricing Model    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Assets 5,000,000 0
Liabilities (131,000,000) (177,000,000)
Total $ (126,000,000) $ (177,000,000)
Options | Minimum | Option Pricing Model | Natural gas to power correlation    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input 0.15 0.15
Options | Minimum | Option Pricing Model | Power and natural gas volatility    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input 0.05 0.05
Options | Maximum | Option Pricing Model | Natural gas to power correlation    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input 1 1
Options | Maximum | Option Pricing Model | Power and natural gas volatility    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input 11.20 11.20
Options | Arithmetic Average | Option Pricing Model | Natural gas to power correlation    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input 0.58 0.58
Options | Arithmetic Average | Option Pricing Model | Power and natural gas volatility    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input 5.63 5.63
Financial transmission rights/Congestion revenue rights | Market Approach    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Assets $ 196,000,000 $ 277,000,000
Liabilities (28,000,000) (34,000,000)
Total 168,000,000 243,000,000
Financial transmission rights/Congestion revenue rights | Minimum | Market Approach | Illiquid price differences between settlement points    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount (45) (12)
Financial transmission rights/Congestion revenue rights | Maximum | Market Approach | Illiquid price differences between settlement points    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 20 25
Financial transmission rights/Congestion revenue rights | Arithmetic Average | Market Approach | Illiquid price differences between settlement points    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount (12.5) 7
Natural gas | Income Approach    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Assets 25,000,000 16,000,000
Liabilities (19,000,000) (24,000,000)
Total 6,000,000 (8,000,000)
Natural gas | Minimum | Income Approach | Natural gas basis    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount (2) (2)
Natural gas | Minimum | Income Approach | Illiquid delivery periods    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 3 3
Natural gas | Maximum | Income Approach | Natural gas basis    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 16 14
Natural gas | Maximum | Income Approach | Illiquid delivery periods    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 5 5
Natural gas | Arithmetic Average | Income Approach | Natural gas basis    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 7 6
Natural gas | Arithmetic Average | Income Approach | Illiquid delivery periods    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Derivative asset (liability), measurement input amount 4 4
Other    
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]    
Assets 8,000,000 11,000,000
Liabilities 0 0
Total $ 8,000,000 $ 11,000,000