OPERATING REVENUES - DISAGGREGATION OF ELECTRIC UTILITY OPERATING REVENUES BY CUSTOMER CLASS (Details) - Revenues from contracts with customers - Utility segment - Transferred over time - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 409.6	$ 338.1	$ 907.1	$ 764.1
Electric
Disaggregation of Operating Revenues
Revenues from contracts with customers	340.6	286.8	680.5	587.1
Electric | Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	308.2	265.0	617.2	539.9
Electric | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	120.7	103.8	252.7	218.2
Electric | Small commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	112.6	98.4	221.6	198.0
Electric | Large commercial and industrial customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	72.6	60.7	138.5	119.4
Electric | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	2.3	2.1	4.4	4.3
Electric | Wholesale
Disaggregation of Operating Revenues
Revenues from contracts with customers	14.8	14.0	28.4	28.6
Electric | Resale
Disaggregation of Operating Revenues
Revenues from contracts with customers	13.5	4.6	26.9	12.6
Electric | Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 4.1	$ 3.2	$ 8.0	$ 6.0