OPERATING REVENUES - DISAGGREGATION OF NATURAL GAS UTILITY OPERATING REVENUES BY CUSTOMER CLASS (Details) - Utility - Revenues from contracts with customers - Transferred over time - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 1,782.0	$ 1,515.5	$ 1,406.4
Natural gas
Disaggregation of Operating Revenues
Revenues from contracts with customers	465.5	338.8	269.5
Natural gas | Total retail revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	446.9	324.0	240.3
Natural gas | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	271.8	202.0	156.4
Natural gas | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	175.1	122.0	83.9
Natural gas | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	20.1	19.4	19.6
Natural gas | Other utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ (1.5)	$ (4.6)	$ 9.6