OPERATING REVENUES ELECTRIC 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
Electric
Disaggregation of Operating Revenues
Revenues from contracts with customers	840.9	877.0	2,343.4	2,441.2
Electric | Total retail
Disaggregation of Operating Revenues
Revenues from contracts with customers	783.2	812.7	2,145.2	2,219.0
Electric | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	345.8	352.7	914.9	929.1
Electric | Small commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	277.7	276.9	764.7	775.2
Electric | Large commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	155.0	177.9	450.4	499.2
Electric | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	4.7	5.2	15.2	15.5
Electric | Wholesale
Disaggregation of Operating Revenues
Revenues from contracts with customers	24.4	28.3	73.4	85.7
Electric | Resale
Disaggregation of Operating Revenues
Revenues from contracts with customers	22.8	31.0	95.9	111.8
Electric | Steam
Disaggregation of Operating Revenues
Revenues from contracts with customers	2.4	2.6	16.8	16.9
Electric | Other utility
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 8.1	$ 2.4	$ 12.1	$ 7.8