v3.26.3
LONG-TERM DEBT - CONVERTIBLE DEBT (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Debt Instrument [Line Items]        
Interest expense $ 241.7 $ 223.6 $ 699.1 $ 667.4
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2027        
Debt Instrument [Line Items]        
Senior Notes 862.5   862.5  
Unamortized debt issuance costs (2.2)   (2.2)  
Net carrying amount 860.3   860.3  
Fair value amount 922.6   922.6  
Contractual interest expense 9.4 9.4 28.3 28.3
Amortization of debt issuance costs 0.8 0.8 2.5 2.5
Interest expense 10.2 10.2 30.8 30.8
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028        
Debt Instrument [Line Items]        
Senior Notes 900.0   900.0  
Unamortized debt issuance costs (5.9)   (5.9)  
Net carrying amount 894.1   894.1  
Fair value amount 890.1   890.1  
Contractual interest expense 7.6 7.6 22.8 9.4
Amortization of debt issuance costs 0.8 0.6 2.6 0.9
Interest expense 8.4 8.2 25.4 10.3
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2029        
Debt Instrument [Line Items]        
Senior Notes 862.5   862.5  
Unamortized debt issuance costs (5.3)   (5.3)  
Net carrying amount 857.2   857.2  
Fair value amount 955.2   955.2  
Contractual interest expense 9.4 9.4 28.3 28.3
Amortization of debt issuance costs 0.5 0.5 1.5 1.5
Interest expense $ 9.9 $ 9.9 $ 29.8 $ 29.8