Operating Revenues - Disaggregation of Electric Utility Operating Revenues by Customer Class (Details) - Revenues from contracts with customers - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 8,235.7	$ 7,169.3	$ 7,449.3
Electric
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,516.6	4,266.1	4,307.7
Wisconsin | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	6,006.9	5,461.7	5,631.8
Wisconsin | Electric | Transferred over time
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,516.6	4,266.1	4,307.7
Wisconsin | Electric | Transferred over time | Total retail revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	4,144.9	3,920.3	3,894.7
Wisconsin | Electric | Transferred over time | Residential
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,768.0	1,743.9	1,608.6
Wisconsin | Electric | Transferred over time | Small commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	1,415.7	1,325.9	1,384.6
Wisconsin | Electric | Transferred over time | Large commercial and industrial
Disaggregation of Operating Revenues
Revenues from contracts with customers	931.9	821.5	871.9
Wisconsin | Electric | Transferred over time | Other
Disaggregation of Operating Revenues
Revenues from contracts with customers	29.3	29.0	29.6
Wisconsin | Electric | Transferred over time | Wholesale
Disaggregation of Operating Revenues
Revenues from contracts with customers	157.7	174.0	189.5
Wisconsin | Electric | Transferred over time | Resale
Disaggregation of Operating Revenues
Revenues from contracts with customers	161.9	130.4	163.1
Wisconsin | Electric | Transferred over time | Steam
Disaggregation of Operating Revenues
Revenues from contracts with customers	28.7	21.3	23.3
Wisconsin | Electric | Transferred over time | Other utility revenues
Disaggregation of Operating Revenues
Revenues from contracts with customers	$ 23.4	$ 20.1	$ 37.1