CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Accounts receivable and unbilled revenues, reserves	$ 200.6	$ 198.3
Property, plant, and equipment, accumulated depreciation and amortization	$ 10,041.4	$ 9,889.3
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	325,000,000	325,000,000
Common stock, shares outstanding	315,434,531	315,434,531
Regulatory assets (March 31, 2022 and December 31, 2021 include $98.2 and $100.7, respectively, related to WEPCo Environmental Trust)	$ 3,163.6	$ 3,264.8
WEPCo Environmental Trust
Regulatory assets (March 31, 2022 and December 31, 2021 include $98.2 and $100.7, respectively, related to WEPCo Environmental Trust)	98.2	100.7
Current portion of long-term debt (March 31, 2022 and December 31, 2021 include $8.8, related to WEPCo Environmental Trust)	8.8	8.8
Long-term debt (March 31, 2022 and December 31, 2021 include $102.8 and $102.7, respectively, related to WEPCo Environmental Trust)	$ 102.8	$ 102.7