v3.26.3
SEGMENT INFORMATION (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
numberOfSegments
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Segment Reporting [Abstract]          
Number of reportable segments | numberOfSegments     2    
Segment information          
External revenues $ 482.7 $ 466.3 $ 1,454.5 $ 1,375.5  
Fuel and purchased power 110.0 106.7 309.5 295.0  
Cost of natural gas sold 7.3 19.9 171.6 145.3  
Other operation and maintenance 119.3 123.3 368.8 364.4  
Depreciation and amortization 70.3 67.4 208.3 199.9  
Property and revenue taxes 12.7 11.1 38.5 33.5  
Other income, net 8.0 5.3 25.0 13.8  
Interest expense 25.5 24.4 73.2 72.6  
Income tax expense 23.9 22.5 48.7 51.3  
Net income 121.7 96.3 260.9 227.3  
Capital expenditures, including AFUDC-Debt 198.5 280.9 522.5 536.6  
Equity method investments 19.7 17.3 19.7 17.3  
Total assets 8,388.2 7,747.4 8,388.2 7,747.4 $ 8,054.6
Utility          
Segment information          
External revenues 482.7 466.3 1,454.5 1,375.5  
Fuel and purchased power 110.0 106.7 309.5 295.0  
Cost of natural gas sold 7.3 19.9 171.6 145.3  
Other operation and maintenance 119.3 123.3 368.8 364.4  
Depreciation and amortization 70.3 67.4 208.3 199.9  
Property and revenue taxes 12.7 11.1 38.5 33.5  
Other income, net 7.4 4.8 23.1 12.3  
Interest expense 25.5 24.4 73.2 72.6  
Income tax expense 23.8 22.3 48.2 50.9  
Net income 121.2 96.0 259.5 226.2  
Capital expenditures, including AFUDC-Debt 198.5 280.9 522.5 536.6  
Equity method investments 0.9 0.9 0.9 0.9  
Total assets 8,369.4 7,731.0 8,369.4 7,731.0  
Other          
Segment information          
External revenues 0.0 0.0 0.0 0.0  
Fuel and purchased power 0.0 0.0 0.0 0.0  
Cost of natural gas sold 0.0 0.0 0.0 0.0  
Other operation and maintenance 0.0 0.0 0.0 0.0  
Depreciation and amortization 0.0 0.0 0.0 0.0  
Property and revenue taxes 0.0 0.0 0.0 0.0  
Other income, net 0.6 0.5 1.9 1.5  
Interest expense 0.0 0.0 0.0 0.0  
Income tax expense 0.1 0.2 0.5 0.4  
Net income 0.5 0.3 1.4 1.1  
Capital expenditures, including AFUDC-Debt 0.0 0.0 0.0 0.0  
Equity method investments 18.8 16.4 18.8 16.4  
Total assets $ 18.8 $ 16.4 $ 18.8 $ 16.4