OPERATING REVENUES - OTHER NON-UTILITY OPERATING REVENUES (Details) - Revenues from contracts with customers - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 1,733.0	$ 1,638.6	$ 6,056.3	$ 5,268.5
Other non-utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	22.4	17.9	73.4	55.7
Other non-utility revenues | We Power revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	5.9	5.8	17.5	17.1
Other non-utility revenues | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.5	0.0	1.8
Transferred over time | Other non-utility revenues | Wind generation revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	12.2	7.4	42.5	24.0
Transferred over time | Other non-utility revenues | Appliance service repairs
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 4.3	$ 4.2	$ 13.4	$ 12.8