v3.25.4
Variable Interest Entity: (Details)
$ in Millions
 12 Months Ended
Apr. 14, 2016
Dec. 31, 2025
USD ($)
MW
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Variable Interest Entity [Line Items]        
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage 49.90%      
Net income attributable to non-controlling interest   $ (8.2) $ (10.6) $ (13.8)
Number of Days Following the End of the Quarter When Distributions of Net Income Attributable to this Non-controlling Interest are Due     30 days  
Current assets   995.9 $ 742.3  
Property, plant and equipment, net   8,234.2 7,629.9  
Current liabilities   740.0 763.4  
Variable Interest Entity, Primary Beneficiary        
Variable Interest Entity [Line Items]        
Assets relating to captive insurance   16.0    
Net income attributable to non-controlling interest   (10.5)    
Current assets   9.6 11.7  
Property, plant and equipment, net   156.9 160.4  
Current liabilities   5.8 8.3  
Power Generation        
Variable Interest Entity [Line Items]        
Net income attributable to non-controlling interest   $ (8.2) $ (10.6) $ (13.8)
Pueblo Airport Generation | Subsidiary of Common Parent        
Variable Interest Entity [Line Items]        
Electric Generation Capacity, Megawatts | MW   200