OPERATING REVENUES NATURAL GAS UTILITY OPERATING REVENUES (Details) - Revenues from contracts with customers - Utility segment - Transferred over time - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 321.0	$ 349.4	$ 715.6	$ 742.1
Natural gas
Disaggregation of Operating Revenues
Revenues from contracts with customers	56.4	56.9	174.0	167.5
Natural gas | Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	46.7	41.8	166.7	156.5
Natural gas | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	30.7	26.5	104.4	97.2
Natural gas | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	16.0	15.3	62.3	59.3
Natural gas | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	3.9	4.0	9.2	12.0
Natural gas | Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 5.8	$ 11.1	$ (1.9)	$ (1.0)