v3.26.3
Debt (Narrative) (Details)
$ in Millions
9 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Debt Instrument [Line Items]      
Long-term Line of Credit $ 0.0   $ 0.0
Proceeds from Issuance of Long-term Debt 0.0 $ 375.0  
Deferred Finance Costs, Net, Including Acquisition Adjustments (8.3)   (9.1)
Debt Instrument, Unamortized Discount (Premium), Net (2.3)   (2.5)
Long-term Debt 1,385.7   1,384.8
Line of Credit Facility, Maximum Borrowing Capacity 350.0    
Long-Term Debt, Current Maturities (139.9)   (0.2)
Long-term debt 1,245.8   1,384.6
3.95% Senior Notes due 2049 [Member]      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 425.0   425.0
Debt Instrument, Interest Rate, Effective Percentage 3.95%    
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Debt Covenant, Total Debt to Total Capitalization Ratio, Maximum 0.67    
Uncommitted Accordion Feature $ 150.0    
Debt Covenant, Total Debt to Total Capitalization Ratio, Maximum Upper 1.00    
3.25% First Mortgage Bonds due 2040 [Member]      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 140.0   140.0
Debt Instrument, Interest Rate, Effective Percentage 3.20%    
U.S. Government note maturing in February 2061 - 4.20% [Member]      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 16.3   16.4
Debt instrument interest percentage 4.20%    
4.25% Tax-exempt First Mortgage Bonds due 2027      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 100.0   100.0
Debt Instrument, Interest Rate, Effective Percentage 4.25%    
4.00% Tax-exempt First Mortgage Bonds due 2027      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 40.0   40.0
Debt Instrument, Interest Rate, Effective Percentage 4.00%    
5.49% Tax-exempt First Mortgage Bonds due 2028      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Effective Percentage 5.49%    
5.49% Senior Notes due 2028      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 92.5   92.5
4.55% First Mortgage Bond Due 2030      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 375.0   375.0
Debt Instrument, Interest Rate, Effective Percentage 4.55%    
5.19% First Mortgage Bonds due 2033      
Debt Instrument [Line Items]      
Long-term Debt, Gross $ 100.0   $ 100.0
Debt Instrument, Interest Rate, Effective Percentage 5.19%    
5.70% Tax-exempt First Mortgage Bonds due 2033      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Effective Percentage 5.70%