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COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details)
$ in Millions
 1 Months Ended 9 Months Ended
Dec. 31, 2024
USD ($)
performance_obligations
Nov. 30, 2024
performance_obligations
May 31, 2024
MMBTU
performance_obligations
Feb. 29, 2024
micrograms
Aug. 31, 2023
Dec. 31, 2020
micrograms
Sep. 30, 2025
USD ($)
performance_obligations
MW
Jun. 30, 2025
performance_obligations
Mar. 31, 2025
numberOfActions
Environmental matters                  
Number of federal deregulatory actions that the EPA announced it will take | numberOfActions                 31
Manufactured gas plant remediation                  
Regulatory assets | $ $ 3,378.7           $ 3,241.0    
Environmental remediation costs                  
Manufactured gas plant remediation                  
Regulatory assets | $ $ 570.1           $ 522.7    
Cross State Air Pollution Rule - Good Neighbor Rule | Electric | Maximum                  
Air quality                  
RICE Unit megawatts | MW             25    
Mercury and Air Toxics Standards | Electric                  
Air quality                  
Previous limit of particulate matter, in pounds per million british thermal unit | MMBTU     0.03            
New limit for particulate matter published in the EPA's 2024 Final Action, in pounds per million british thermal unit | MMBTU     0.01            
National Ambient Air Quality Standards | Electric                  
Air quality                  
Number of volumes of the Integrated Review Plan the EPA released 2                
Current level of micrograms per cubic meter that particulate matter needs to be below | micrograms           12      
Current level of micrograms per cubic meter under 24-hour standard that particulate matter needs to be below | micrograms           35      
National Ambient Air Quality Standards | Electric | Maximum                  
Air quality                  
Period of time for EPA review of ozone plan         5 years        
New primary annual PM2.5 level | micrograms       9          
National Ambient Air Quality Standards | Electric | Minimum                  
Air quality                  
Period of time for EPA review of ozone plan         3 years        
Number of years between evaluation of attainment status         3 years        
Climate Change | Electric                  
Air quality                  
Number of applicable GHG performance standards for coal plants             0    
Percent capacity factor that if combined cycle natural gas plants are above, it causes the rule to be dependent upon the implementation of carbon capture             40.00%    
Number of applicable GHG limits for new simple cycle natural gas-fired combustion turbines             0    
Percent capacity factor for simple cycle natural gas fired combustion turbines that there are no applicable limits if the capacity factor is less than this             20.00%    
Number of proposed rule packages the EPA is releasing to address NOx emissions from existing combustion turbines   3              
Percent capacity factor for turbines that will require more stringent NOX limits   20.00%              
Percent capacity factor for turbines that below this percentage will have less restrictive standards   20.00%              
Number of potential regulatory paths the EPA is co-proposing               2  
Capacity of fossil-fueled generation retired, in megawatts | MW             2,500    
Capacity of coal-fired generation to be retired by the end of 2031, in megawatts | MW             900    
Climate Change | Electric | Maximum                  
Air quality                  
RICE Unit megawatts | MW             25    
Steam Electric Effluent Limitation Guidelines | Electric                  
Water quality                  
Number of new ELG rule requirements that affect our electric utilities     3            
Compliance costs associated with the ELG rule that were required to achieve discharge limits | $             $ 105.0    
Number of existing coal categories that were kept as part of the 2024 supplemental ELG rule requirements     1            
Number of new coal categories that were created as part of the 2024 supplemental ELG rule requirements     1            
Manufactured Gas Plant Remediation | Natural gas                  
Manufactured gas plant remediation                  
Reserves for future environmental remediation | $ $ 445.8           438.2    
Manufactured Gas Plant Remediation | Natural gas | Environmental remediation costs                  
Manufactured gas plant remediation                  
Regulatory assets | $ $ 570.1           $ 522.7