VARIABLE INTEREST ENTITIES - WEPCO ENVIRONMENTAL TRUST (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2020	Mar. 31, 2024	Dec. 31, 2023
Assets
Other current assets (restricted cash)		$ 43.6	$ 70.1
Regulatory assets		3,247.0	3,249.8
Other long-term assets (restricted cash)		33.6	52.2
Liabilities
Accounts payable		640.9	896.6
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)		3.2	0.8
Regulatory assets		84.1	85.9
Other long-term assets (restricted cash)		0.6	0.6
Liabilities
Current portion of long-term debt		9.0	9.0
Accounts payable		0.1	0.0
Other current liabilities (accrued interest)		0.5	0.1
Long-term debt		$ 85.4	$ 85.3