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VARIABLE INTEREST ENTITIES - WEPCO ENVIRONMENTAL TRUST (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2020	Sep. 30, 2021	Dec. 31, 2020
Assets
Other current assets (restricted cash)		$ 36.4	$ 0.0
Regulatory assets		3,488.7	3,524.1
Other long-term assets (restricted cash)		46.8	$ 47.8
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)		4.6
Regulatory assets		102.9
Other long-term assets (restricted cash)		0.6
Liabilities
Current portion of long-term debt		8.5
Other current liabilities (accrued interest)		0.7
Long-term debt		$ 107.0