VARIABLE INTEREST ENTITIES - WEPCO ENVIRONMENTAL TRUST (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Nov. 01, 2020
Assets
Other current assets (restricted cash)	$ 11.2	$ 70.1
Regulatory assets	3,346.5	3,249.8
Other long-term assets (restricted cash)	27.3	52.2
Liabilities
Current portion of long-term debt	1,823.7	1,264.2
Other current liabilities (accrued interest)	202.4	154.4
WEPCo Environmental Trust
Variable interest entities
Securitization of environmental control costs related to Pleasant Prairie power plant			$ 100.0
Assets
Other current assets (restricted cash)	3.3	0.8
Regulatory assets	79.1	85.9
Other long-term assets (restricted cash)	0.3	0.6
Liabilities
Current portion of long-term debt	9.1	9.0
Other current liabilities (accrued interest)	0.4	0.1
Long-term debt	$ 80.9	$ 85.3