Variable Interest Entities - WEPCo Environmental Trust (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets
Other current assets (restricted cash)		$ 70.1	$ 25.6	$ 19.6
Regulatory assets		3,249.8	3,264.6
Other long-term assets (restricted cash)		52.2	127.7	$ 51.6
Liabilities
Current portion of long-term debt		1,264.2	808.5
Long-term debt		15,366.9	14,655.7
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)		0.8	3.0
Regulatory assets		85.9	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)		0.1	0.1
Long-term debt		$ 85.3	$ 94.1