v3.26.3
Summary of Significant Accounting Policies (Narrative) (Details)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Jun. 30, 2026
USD ($)
Mar. 31, 2026
USD ($)
Sep. 30, 2025
USD ($)
Jun. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Sep. 30, 2026
USD ($)
mi²
segment
customer
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Apr. 04, 2025
Dec. 31, 2024
USD ($)
Significant Accounting Policies [Line Items]                      
Number of reportable segments | segment             1        
Cash and Cash Equivalent $ 67.5           $ 67.5   $ 60.7    
Restricted Cash 0.1           $ 0.1   0.1    
Approximate number of retail customers | customer             546,000        
Service area, square miles | mi²             6,000        
Number of Operating Segments | segment             1        
Excise taxes collected 14.4     $ 13.7     $ 38.4 $ 38.0      
Customer receivables 151.1           151.1   116.5    
Unbilled Revenue 31.0           31.0   40.9    
Accounts Receivable, Allowance for Credit Loss (9.6)     (8.9)     (9.6) (8.9) (8.8)   $ (6.1)
Accounts Receivable, Allowance for Credit Loss, Current 9.6           9.6        
Accounts Receivable, Credit Loss Expense (Reversal)             11.7 8.9      
Accounts Receivable, Allowance for Credit Loss, Writeoff             (11.0) (6.1)      
Accounts Receivable, Allowance for Credit Loss, Recovery             0.1 0.0      
Interest expense (14.9)     (14.6)     (45.1) (43.0)      
Income Tax Expense (Benefit) (12.5)     (10.9)     (27.5) (16.6)      
Nonoperating Income (Expense), Total (14.9)     (15.2)     (44.3) (45.3)      
Accumulated other comprehensive income (21.1)           (21.1)   (22.3)    
Other Comprehensive Income (Loss), Net of Tax 0.4 $ 0.4 $ 0.4 0.5 $ 0.5 $ 0.5 1.2 1.5      
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax 0.4     0.5     1.2 1.5      
Contract with Customer, Asset, before Allowance for Credit Loss 182.1           182.1   157.4    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 67.6     78.8     67.6 78.8 60.8   $ 24.7
Accounts Receivable, after Allowance for Credit Loss, Current 178.3           178.3   160.7    
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax (0.1)     (0.2)     (0.4) (0.4)      
Allowance for Funds Used During Construction, Equity Portion 1.6     0.2     3.5 0.3      
Allowance for Funds Used During Construction, Capitalized Interest (1.1)     (1.5)     (2.5) (4.4)      
Unrealized Gain (Loss) on Investments (0.1)     $ 0.4     0.1 $ 0.6      
Ohio Holdings Investment Percent         100.00%            
CDPQ Investment percent                   30.00%  
Property, Plant, and Equipment [Line Items]                      
Property, Plant, and Equipment, Accumulated Depreciation, Depletion, and Amortization (1,204.4)           (1,204.4)   (1,172.4)    
Property, Plant, and Equipment, after Accumulated Depreciation, Depletion, and Amortization 3,135.1           3,135.1   2,859.4    
Contributions in Aid of Construction 58.0           58.0   27.0    
Nonrelated Party                      
Significant Accounting Policies [Line Items]                      
Other 2.2           2.2   9.9    
Related Party                      
Significant Accounting Policies [Line Items]                      
Other $ 3.6           $ 3.6   $ 2.2