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CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Statement of Financial Position [Abstract]    
Accounts receivable and unbilled revenues, reserves $ 139.9 $ 148.7
Property, plant, and equipment, accumulated depreciation and amortization $ 13,025.9 $ 12,411.5
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Common stock, shares authorized 650,000,000 650,000,000
Common stock, shares outstanding 328,992,329 325,461,519
Regulatory assets (September 30, 2026 and December 31, 2025 include $60.9 and $67.5, respectively, related to WEPCo Environmental Trust) $ 3,140.7 $ 3,156.3
Current portion of long-term debt (September 30, 2026 and December 31, 2025 include $9.4 and $9.3, respectively, related to WEPCo Environmental Trust) 1,134.5 1,519.4
Long-term debt (September 30, 2026 and December 31, 2025 include $62.8 and $67.4, respectively, related to WEPCo Environmental Trust) 19,717.2 18,498.1
WEPCo Environmental Trust    
Regulatory assets (September 30, 2026 and December 31, 2025 include $60.9 and $67.5, respectively, related to WEPCo Environmental Trust) 60.9 67.5
Current portion of long-term debt (September 30, 2026 and December 31, 2025 include $9.4 and $9.3, respectively, related to WEPCo Environmental Trust) 9.4 9.3
Long-term debt (September 30, 2026 and December 31, 2025 include $62.8 and $67.4, respectively, related to WEPCo Environmental Trust) $ 62.8 $ 67.4