OPERATING REVENUES - OTHER NON-UTILITY OPERATING REVENUES (Details) - Revenues from contracts with customers - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 1,654.3	$ 1,543.0	$ 4,323.3	$ 3,629.9
Other non-utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	24.7	18.2	51.0	37.8
Other non-utility revenues | We Power revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	5.8	5.8	11.6	11.3
Other non-utility revenues | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.0	0.9	0.0	1.3
Transferred over time | Other non-utility revenues | Wind generation revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	14.5	7.3	30.3	16.6
Transferred over time | Other non-utility revenues | Appliance service repairs
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 4.4	$ 4.2	$ 9.1	$ 8.6