OPERATING REVENUES - OTHER NON-UTILITY OPERATING REVENUES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
We Power revenues
Disaggregation of Operating Revenues
Revenues amortized from deferred revenue during the period	$ 6.4	$ 6.4
Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	2,376.5	2,290.0
Other non-utility revenues | Revenues from contracts with customers
Disaggregation of Operating Revenues
Revenues from contracts with customers	18.3	11.6
Other non-utility revenues | Revenues from contracts with customers | We Power revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	6.4	6.4
Other non-utility revenues | Revenues from contracts with customers | Distributed renewable solar project revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	1.5	1.3
Other non-utility revenues | Revenues from contracts with customers | Wind generation revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	6.2	0.0
Other non-utility revenues | Revenues from contracts with customers | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	0.1	0.0
Transferred over time | Other non-utility revenues | Revenues from contracts with customers | Appliance service repairs
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 4.1	$ 3.9
Upstream
Disaggregation of Operating Revenues
WEC's ownership interest in Upstream Wind Energy Center	80.00%
Number of years Upstream will receive fixed payment	10 years