Variable Interest Entities - WEPCo Environmental Trust (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Variable interest entities
Other current assets (restricted cash)		$ 19.6	$ 0.0	$ 0.0
Regulatory assets		3,264.8	3,524.1
Other long-term assets (restricted cash)		51.6	47.8	$ 44.8
Current portion of long-term debt		91.0	777.7
Long-term debt		13,472.4	$ 11,672.8
WEPCo Environmental Trust
Variable interest entities
Securitized Regulatory Asset	$ 100.0
Other current assets (restricted cash)		2.4
Regulatory assets		100.7
Other long-term assets (restricted cash)		0.6
Current portion of long-term debt		8.8
Other current liabilities (accrued interest)		0.1
Long-term debt		$ 102.7