VARIABLE INTEREST ENTITIES - WEPCO ENVIRONMENTAL TRUST (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2020	Sep. 30, 2023	Dec. 31, 2022
Assets
Other current assets (restricted cash)		$ 43.6	$ 25.6
Regulatory assets		3,197.1	3,264.6
Other long-term assets (restricted cash)		51.9	127.7
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)		3.9	3.0
Regulatory assets		87.5	92.4
Other long-term assets (restricted cash)		0.6	0.6
Liabilities
Current portion of long-term debt		9.0	8.9
Other current liabilities (accrued interest)		0.5	0.1
Long-term debt		$ 89.8	$ 94.1