v3.26.1
Summary of Significant Accounting Policies (Narrative) (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2026
USD ($)
mi²
customer
segment
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Dec. 31, 2024
USD ($)
Significant Accounting Policies [Line Items]        
Number of reportable segments | segment 1      
Cash and Cash Equivalent $ 69.9   $ 82.9  
Restricted Cash 0.1   0.1  
Excise taxes collected 12.9 $ 13.2    
Customer receivables 143.6   117.3  
Unbilled Revenue 31.0   40.9  
Accounts Receivable, Allowance for Credit Loss (11.9) (8.1) (8.8) $ (6.1)
Accounts Receivable, after Allowance for Credit Loss     161.1  
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 (20.0) (23.9)    
Income Tax Expense (Benefit) (12.6) (1.0)    
Net income (39.3) (2.7)    
Nonoperating Income (Expense) 19.7 24.5    
Accumulated other comprehensive income 15.5 (5.3) 15.7 (5.3)
Other Comprehensive Income (Loss), Net of Tax (0.1) 0.0    
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax (0.2)      
Contract with Customer, Asset, before Allowance for Credit Loss 174.6   158.2  
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 70.0 81.3 83.0 $ 54.1
Accounts Receivable, after Allowance for Credit Loss, Current 166.1   161.1  
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax (0.2) (0.2)    
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax (0.2) (0.0)    
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax (0.0) (0.0)    
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, after Accumulated Depreciation, Depletion, and Amortization 2,950.5   2,885.8  
Property, Plant, and Equipment, Accumulated Depreciation, Depletion, and Amortization (669.2)   (647.3)  
Nonrelated Party        
Significant Accounting Policies [Line Items]        
Other 1.7   10.0  
Related Party        
Significant Accounting Policies [Line Items]        
Other $ 1.7   $ 1.7  
Subsidiaries [Member]        
Significant Accounting Policies [Line Items]        
Approximate number of retail customers | customer 540,000      
Service area, square miles | mi² 6,000