OPERATING REVENUES NATURAL GAS UTILITY OPERATING REVENUES (Details) - Revenues from contracts with customers - Utility segment - Transferred over time - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 882.2	$ 922.4	$ 2,627.3	$ 2,716.0
Natural gas
Disaggregation of Operating Revenues
Revenues from contracts with customers	41.3	45.4	283.9	274.8
Natural gas | Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	27.8	28.9	263.8	258.1
Natural gas | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	20.5	20.8	181.5	176.2
Natural gas | Commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	7.3	8.1	82.3	81.9
Natural gas | Transport
Disaggregation of Operating Revenues
Revenues from contracts with customers	2.5	2.2	9.7	9.7
Natural gas | Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 11.0	$ 14.3	$ 10.4	$ 7.0