v3.26.3
Business Segments (Segment Financial Information) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Jun. 30, 2026
Mar. 31, 2026
Sep. 30, 2025
Jun. 30, 2025
Mar. 31, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]                  
Revenues $ 353.2     $ 292.7     $ 958.3 $ 772.4  
Depreciation and amortization 30.0     29.4     92.4 87.2  
Interest expense 14.9     14.6     45.1 43.0  
Total assets 3,883.5           3,883.5   $ 3,730.8
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 54.5     27.8     122.2 49.7  
Purchased power 128.6     113.6     340.4 290.9  
Operation and maintenance 84.7     70.4     241.4 199.1  
Taxes other than income taxes 40.5     36.3     117.6 100.2  
Other Nonoperating Income (Expense) 0.0     (0.6)     0.8 (2.3)  
Income Tax Expense (Benefit) 12.5     10.9     27.5 16.6  
Net Income (Loss) Attributable to Parent, Total 42.0 $ 10.5 $ 42.2 16.9 $ 5.5 $ 10.7 94.7 33.1  
Operating Segments [Member]                  
Segment Reporting [Line Items]                  
Revenues             958.3    
Depreciation and amortization             92.4    
Interest expense             45.1    
Purchased power             340.4    
Operation and maintenance             241.4    
Taxes other than income taxes             117.6    
Segment Reporting, Other Segment Item, Amount             (0.8)    
Operating Segments [Member] | Utility [Member]                  
Segment Reporting [Line Items]                  
Revenues 353.2     292.7       772.4  
Depreciation and amortization 30.0     29.4       87.2  
Interest expense 14.9     14.6       43.0  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 54.5     27.8     122.2 49.7  
Purchased power 128.6     113.6       290.9  
Operation and maintenance 84.7     70.4       199.1  
Taxes other than income taxes 40.5     36.3       100.2  
Income Tax Expense (Benefit) 12.5     10.9     27.5 16.6  
Net Income (Loss) Attributable to Parent, Total 42.0     16.9     94.7 33.1  
Segment Reporting, Other Segment Item, Amount 0.0     0.6       2.3  
Segment Reporting, Long-Lived Asset, Expenditure for Addition $ 148.2     $ 98.6     $ 365.2 $ 256.1