v3.26.1
Summary of Significant Accounting Policies (Narrative) (Details)
$ in Millions
3 Months Ended
Mar. 31, 2026
USD ($)
mi²
segment
customer
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Dec. 31, 2024
USD ($)
Significant Accounting Policies [Line Items]        
Number of reportable segments | segment 1      
Cash and Cash Equivalent $ 41.4   $ 60.7  
Restricted Cash $ 0.1   0.1  
Approximate number of retail customers | customer 540,000      
Service area, square miles | mi² 6,000      
Number of Operating Segments | segment 1      
Excise taxes collected $ 12.9 $ 13.2    
Customer receivables 143.0   116.5  
Unbilled Revenue 31.0   40.9  
Accounts Receivable, Allowance for Credit Loss (11.9) (8.1) (8.8) $ (6.1)
Accounts Receivable, Allowance for Credit Loss, Current 11.9      
Accounts Receivable, Credit Loss Expense (Reversal) 6.2 1.8    
Accounts Receivable, Allowance for Credit Loss, Writeoff (3.2) (0.1)    
Accounts Receivable, Allowance for Credit Loss, Recovery 0.1 0.3    
Interest expense (15.4) (14.7)    
Income Tax Expense (Benefit) (12.2) (1.7)    
Nonoperating Income (Expense) 15.6 16.0    
Accumulated other comprehensive income (21.9) (25.9) (22.3) (26.4)
Other Comprehensive Income (Loss), Net of Tax 0.4 0.5    
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax (0.4) (0.5)    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 41.5 60.5 60.8 $ 24.7
Accounts Receivable, after Allowance for Credit Loss, Current 166.1   160.7  
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax (0.2) (0.1)    
Allowance for Funds Used During Construction, Equity Portion 0.7 0.0    
Allowance for Funds Used During Construction, Capitalized Interest (0.4) (1.4)    
Unrealized Gain (Loss) on Investments (0.2) $ (0.1)    
Property, Plant, and Equipment [Line Items]        
Property, Plant, and Equipment, Accumulated Depreciation, Depletion, and Amortization (1,189.8)   (1,172.4)  
Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization 2,924.4   2,859.4  
Nonrelated Party        
Significant Accounting Policies [Line Items]        
Other 1.7   9.9  
Related Party        
Significant Accounting Policies [Line Items]        
Other 2.3   2.2  
Subsidiaries [Member]        
Significant Accounting Policies [Line Items]        
Contract with Customer, Asset, before Allowance for Credit Loss $ 174.0   $ 157.4