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OPERATING REVENUES - DISAGGREGATION OF OPERATING REVENUES FOR UTILITY SEGMENT (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Operating Revenues        
Total operating revenues $ 1,057.1 $ 1,010.8 $ 2,380.6 $ 2,189.9
Utility segment        
Disaggregation of Operating Revenues        
Total operating revenues 1,057.1 1,010.8 2,380.6 2,189.9
Utility segment | Other operating revenues        
Disaggregation of Operating Revenues        
Other operating revenues 14.2 4.7 23.9 7.7
Utility segment | Transferred over time | Revenues from contracts with customers        
Disaggregation of Operating Revenues        
Revenues from contracts with customers 1,042.9 1,006.1 2,356.7 2,182.2
Utility segment | Electric | Transferred over time | Revenues from contracts with customers        
Disaggregation of Operating Revenues        
Revenues from contracts with customers 963.8 921.3 1,979.5 1,856.6
Utility segment | Natural gas | Transferred over time | Revenues from contracts with customers        
Disaggregation of Operating Revenues        
Revenues from contracts with customers $ 79.1 $ 84.8 $ 377.2 $ 325.6