v3.25.2
Other Comprehensive Income: Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2024
Mar. 31, 2024
Jun. 30, 2025
Jun. 30, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Interest expense $ 49.8   $ 48.2   $ 101.6 $ 94.2
Fuel, purchased power and cost of natural gas sold 124.0   107.1   483.8 423.7
Income tax expense (4.4)   (3.7)   (22.5) (20.6)
Operations and maintenance 147.6   141.7   301.3 275.2
Net income 28.8 $ 136.4 24.7 $ 131.6 165.2 156.2
Reclassification out of Accumulated Other Comprehensive Income            
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Net income (0.7)   (1.0)   (1.6) (3.7)
Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income            
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Income before income taxes (0.9)   (1.3)   (2.0) (4.6)
Income tax expense 0.2   0.3   0.5 1.0
Net income (0.7)   (1.0)   (1.5) (3.6)
Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income | Interest Rate Swap            
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Interest expense (0.8)   (0.7)   (1.4) (1.4)
Cash Flow Hedging | Reclassification out of Accumulated Other Comprehensive Income | Commodity Contract            
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Fuel, purchased power and cost of natural gas sold (0.1)   (0.6)   (0.6) (3.2)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income            
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Operations and maintenance 0.0   0.0   (0.1) (0.1)
Accumulated Defined Benefit Plans Adjustment | Reclassification out of Accumulated Other Comprehensive Income            
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]            
Net income $ 0.0   $ 0.0   $ (0.1) $ (0.1)