v3.25.4
Regulatory Matters: Regulatory Matters (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Regulatory Asset [Line Items]    
Regulatory assets $ 394.7 $ 427.7
Regulatory assets, current (139.7) (154.8)
Regulatory assets, non-current 255.0 272.9
Regulatory liabilities 588.2 568.7
Regulatory liabilities, current (99.9) (94.1)
Regulatory liabilities, non-current $ 488.3 474.6
Maximum    
Regulatory Asset [Line Items]    
Gas Price Derivatives - Term of Contract 2 years  
Deferred energy and fuel cost adjustments    
Regulatory Asset [Line Items]    
Regulatory liabilities $ 12.3 5.8
Deferred gas cost adjustments    
Regulatory Asset [Line Items]    
Regulatory liabilities 51.5 62.0
Employee benefit plans and related deferred taxes    
Regulatory Asset [Line Items]    
Regulatory liabilities 36.2 36.7
Cost of removal    
Regulatory Asset [Line Items]    
Regulatory liabilities 216.5 197.0
Excess deferred income taxes    
Regulatory Asset [Line Items]    
Regulatory liabilities 230.3 238.5
Colorado renewable energy    
Regulatory Asset [Line Items]    
Regulatory liabilities 33.2 24.1
Other regulatory liabilities    
Regulatory Asset [Line Items]    
Regulatory liabilities 8.2 4.6
Storm Costs    
Regulatory Asset [Line Items]    
Regulatory assets 50.7 109.5
Deferred energy and gas costs    
Regulatory Asset [Line Items]    
Regulatory assets 83.3 62.8
Deferred gas cost adjustments    
Regulatory Asset [Line Items]    
Regulatory assets 10.2 14.5
Gas price derivatives    
Regulatory Asset [Line Items]    
Regulatory assets 4.6 2.9
Deferred taxes on AFUDC    
Regulatory Asset [Line Items]    
Regulatory assets 10.6 8.0
Employee benefit plans and related deferred taxes    
Regulatory Asset [Line Items]    
Regulatory assets 87.4 89.0
Environmental    
Regulatory Asset [Line Items]    
Regulatory assets 13.1 10.7
Loss on reacquired debt    
Regulatory Asset [Line Items]    
Regulatory assets 14.1 15.7
Deferred taxes on flow through accounting    
Regulatory Asset [Line Items]    
Regulatory assets 94.8 87.7
Other regulatory assets    
Regulatory Asset [Line Items]    
Regulatory assets $ 25.9 $ 26.9