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, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 338.1	$ 381.3	$ 764.1	$ 871.2
Electric
Disaggregation of Operating Revenues
Revenues from contracts with customers	286.8	319.8	587.1	639.8
Electric | Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	265.0	292.8	539.9	585.3
Electric | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	103.8	113.6	218.2	234.4
Electric | Small commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	98.4	109.1	198.0	213.7
Electric | Large commercial and industrial customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	60.7	67.9	119.4	132.8
Electric | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	2.1	2.2	4.3	4.4
Electric | Wholesale
Disaggregation of Operating Revenues
Revenues from contracts with customers	14.0	20.1	28.6	42.6
Electric | Resale
Disaggregation of Operating Revenues
Revenues from contracts with customers	4.6	4.3	12.6	10.3
Electric | Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 3.2	$ 2.6	$ 6.0	$ 1.6