Variable Interest Entities - WEPCo Environmental Trust (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2020	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Assets
Other current assets (restricted cash)		$ 5.3	$ 70.1	$ 25.6
Regulatory assets		3,339.7	3,249.8
Other long-term assets (restricted cash)		27.1	52.2	$ 127.7
Liabilities
Current portion of long-term debt		1,729.0	1,264.2
Long-term debt		17,178.1	15,366.9
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)		1.5	0.8
Regulatory assets		76.5	85.9
Other long-term assets (restricted cash)		0.6	0.6
Liabilities
Current portion of long-term debt		9.2	9.0
Other current liabilities (accrued interest)		0.1	0.1
Long-term debt		$ 76.4	$ 85.3