SEGMENT INFORMATION (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) segment	Mar. 31, 2022 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	2
Segment information
Operating revenues	$ 491.5	$ 478.9
Other operation and maintenance	107.9	83.7
Depreciation and amortization	55.0	49.7
Other income, net	11.7	10.1
Interest expense	21.8	16.6
Income tax expense	12.6	24.0
Net income	66.3	76.6
Utility
Segment information
Operating revenues	491.5	478.9
Other operation and maintenance	107.9	83.7
Depreciation and amortization	55.0	49.7
Other income, net	11.0	9.7
Interest expense	21.8	16.6
Income tax expense	12.5	23.9
Net income	65.7	76.3
Other
Segment information
Operating revenues	0.0	0.0
Other operation and maintenance	0.0	0.0
Depreciation and amortization	0.0	0.0
Other income, net	0.7	0.4
Interest expense	0.0	0.0
Income tax expense	0.1	0.1
Net income	$ 0.6	$ 0.3