VARIABLE INTEREST ENTITIES - WEPCO ENVIRONMENTAL TRUST (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Nov. 01, 2020
Assets
Other current assets (restricted cash)	$ 11.7	$ 5.3
Regulatory assets	3,231.8	3,339.7
Other long-term assets (restricted cash)	34.5	27.1
Liabilities
Current portion of long-term debt	2,250.4	1,729.0
Long-term debt	17,110.4	17,178.1
WEPCo Environmental Trust Finance I, LLC
Variable interest entities
Securitization of environmental control costs related to Pleasant Prairie power plant			$ 100.0
Assets
Other current assets (restricted cash)	1.4	1.5
Regulatory assets	72.2	76.5
Other long-term assets (restricted cash)	0.6	0.6
Liabilities
Current portion of long-term debt	9.2	9.2
Other current liabilities (accrued interest)	0.1	0.1
Long-term debt	$ 71.9	$ 76.4