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
Total operating revenues	$ 1,364.8	$ 1,201.9	$ 3,745.4	$ 3,391.8
Utility segment
Disaggregation of Operating Revenues
Total operating revenues	1,364.8	1,201.9	3,745.4	3,391.8
Utility segment \| Other operating revenues
Disaggregation of Operating Revenues
Other operating revenues	40.5	2.0	64.4	9.7
Utility segment \| Transferred over time \| Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,324.3	1,199.9	3,681.0	3,382.1
Utility segment \| Electric \| Transferred over time \| Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,275.5	1,146.7	3,255.0	3,003.3
Utility segment \| Natural gas \| Transferred over time \| Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 48.8	$ 53.2	$ 426.0	$ 378.8

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