v3.26.3
OPERATING REVENUES - DISAGGREGATION OF OPERATING REVENUES FOR UTILITY SEGMENT (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Disaggregation of Operating Revenues        
Operating revenues $ 482.7 $ 466.3 $ 1,454.5 $ 1,375.5
Utility segment        
Disaggregation of Operating Revenues        
Operating revenues 482.7 466.3 1,454.5 1,375.5
Utility segment | Other operating revenues        
Disaggregation of Operating Revenues        
Other operating revenues 0.5 0.7 2.7 2.8
Utility segment | Transferred over time | Revenues from contracts with customers        
Disaggregation of Operating Revenues        
Revenues from contracts with customers 482.2 465.6 1,451.8 1,372.7
Utility segment | Electric | Transferred over time | Revenues from contracts with customers        
Disaggregation of Operating Revenues        
Revenues from contracts with customers 445.6 416.3 1,147.6 1,096.8
Utility segment | Natural gas | Transferred over time | Revenues from contracts with customers        
Disaggregation of Operating Revenues        
Revenues from contracts with customers $ 36.6 $ 49.3 $ 304.2 $ 275.9