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LONG-TERM DEBT (Details)
 1 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2025
USD ($)
Aug. 31, 2025
USD ($)
Jun. 30, 2025
USD ($)
d
$ / shares
May 31, 2025
USD ($)
Apr. 30, 2025
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2024
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2024
USD ($)
Debt Instrument [Line Items]                  
Interest expense           $ 223,600,000 $ 204,200,000 $ 667,400,000 $ 596,800,000
3.10% WE Debentures due June 1, 2025 | WE                  
Debt Instrument [Line Items]                  
Repayment of long-term debt     $ 250,000,000.0            
Interest rate on long-term debt     3.10%            
4.15% $500M WE Debentures due 10/15/2030 | WE                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt 4.15%         4.15%   4.15%  
Proceeds from issuance of debt $ 500,000,000.0                
4.70% $175M WG Debentures due 10/1/2030 | WG                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt 4.70%         4.70%   4.70%  
Proceeds from issuance of debt $ 175,000,000.0                
5.39% $125M WG Debentures due 10/1/2035 | WG                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt 5.39%         5.39%   5.39%  
Proceeds from issuance of debt $ 125,000,000.0                
3.53% $200M WG Debentures due 09/30/2025 | WG                  
Debt Instrument [Line Items]                  
Repayment of long-term debt $ 200,000,000.0                
Interest rate on long-term debt 3.53%         3.53%   3.53%  
5.20% MERC Senior Notes due 5/1/2030 | MERC                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt         5.20%        
Proceeds from issuance of debt         $ 50,000,000.0        
2.69% MERC Senior Notes due 5/1/2025 | MERC                  
Debt Instrument [Line Items]                  
Repayment of long-term debt       $ 50,000,000          
Interest rate on long-term debt       2.69%          
5.20% MGU Senior Notes due 5/1/2030 | MGU                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt         5.20%        
Proceeds from issuance of debt         $ 75,000,000.0        
2.69% MGU Senior Notes due 5/1/2025 | MGU                  
Debt Instrument [Line Items]                  
Repayment of long-term debt       $ 60,000,000          
Interest rate on long-term debt       2.69%          
5.31% $80M UMERC Senior Notes due 8/14/2030 | UMERC                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt   5.31%              
Proceeds from issuance of debt   $ 80,000,000.0              
5.93% $40M UMERC Senior Notes due 8/14/2035 | UMERC                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt   5.93%              
Proceeds from issuance of debt   $ 40,000,000.0              
WEC Energy Group | WEC 3.55% Senior Notes $120M due June 15, 2025                  
Debt Instrument [Line Items]                  
Repayment of long-term debt     $ 120,000,000.0            
Interest rate on long-term debt     3.55%            
WEC Energy Group | WEC 5.00% Senior Notes $500M due September 27, 2025                  
Debt Instrument [Line Items]                  
Repayment of long-term debt $ 500,000,000.0                
Interest rate on long-term debt 5.00%         5.00%   5.00%  
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028                  
Debt Instrument [Line Items]                  
Interest rate on long-term debt     3.375%            
Proceeds from convertible debt     $ 900,000,000.0            
Principal amount conversion rate applied to     $ 1,000            
Initial conversion ratio     7.7901            
Initial conversion price, per share | $ / shares     $ 128.37            
Senior Notes $ 900,000,000.0         $ 900,000,000.0   $ 900,000,000.0  
Unamortized debt issuance costs (9,400,000)         (9,400,000)   (9,400,000)  
Net carrying amount 890,600,000         890,600,000   890,600,000  
Fair value amount 928,300,000         928,300,000   928,300,000  
Contractual interest expense           7,600,000 0 9,400,000 0
Amortization of debt issuance costs           600,000 0 900,000 0
Interest expense           8,200,000 0 10,300,000 0
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Early redemption terms                  
Debt Instrument [Line Items]                  
Debt instrument, redemption price, percentage     100.00%            
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Debt conversion terms one                  
Debt Instrument [Line Items]                  
Trading days | d     20            
Consecutive trading days | d     30            
Threshold percentage of trigger     130.00%            
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Debt conversion terms two                  
Debt Instrument [Line Items]                  
Trading days | d     5            
Consecutive trading days | d     10            
Threshold percentage of trigger     98.00%            
Principal amount conversion rate applied to     $ 1,000            
WEC Energy Group | WEC 3.375% Convertible Notes due June 1, 2028 | Debt conversion terms three                  
Debt Instrument [Line Items]                  
Trading days prior to redemption | d     2            
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2027                  
Debt Instrument [Line Items]                  
Senior Notes 862,500,000         862,500,000   862,500,000  
Unamortized debt issuance costs (5,500,000)         (5,500,000)   (5,500,000)  
Net carrying amount 857,000,000.0         857,000,000.0   857,000,000.0  
Fair value amount 1,034,600,000         1,034,600,000   1,034,600,000  
Contractual interest expense           9,400,000 9,400,000 28,300,000 12,900,000
Amortization of debt issuance costs           800,000 800,000 2,500,000 1,100,000
Interest expense           10,200,000 10,200,000 30,800,000 14,000,000.0
WEC Energy Group | WEC 4.375% Convertible Notes due June 1, 2029                  
Debt Instrument [Line Items]                  
Senior Notes 862,500,000         862,500,000   862,500,000  
Unamortized debt issuance costs (7,300,000)         (7,300,000)   (7,300,000)  
Net carrying amount 855,200,000         855,200,000   855,200,000  
Fair value amount $ 1,056,600,000         1,056,600,000   1,056,600,000  
Contractual interest expense           9,400,000 9,400,000 28,300,000 12,900,000
Amortization of debt issuance costs           500,000 500,000 1,500,000 700,000
Interest expense           $ 9,900,000 $ 9,900,000 $ 29,800,000 $ 13,600,000