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COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details)
$ in Millions
 1 Months Ended 9 Months Ended
Aug. 31, 2023
May 31, 2023
MW
performance_obligations
Apr. 30, 2023
MMBTU
Jan. 31, 2023
micrograms
Dec. 31, 2020
micrograms
performance_obligations
Sep. 30, 2023
USD ($)
generating_units
MW
performance_obligations
Jun. 30, 2023
USD ($)
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Manufactured gas plant remediation                  
Regulatory assets | $           $ 3,212.9   $ 3,306.9  
Environmental remediation costs                  
Manufactured gas plant remediation                  
Regulatory assets | $           $ 577.7   610.7  
Cross State Air Pollution Rule - Good Neighbor Plan | Electric | Maximum                  
Air quality                  
RICE Unit megawatts | MW           25      
Mercury and Air Toxics Standards | Electric                  
Air quality                  
Current level of particulate matter in pounds per million british thermal unit | MMBTU     0.03            
EPA proposed lower limit for particulate matter | MMBTU     0.01            
Even lower level of particulate matter that the EPA is seeking opinions on | MMBTU     0.006            
National Ambient Air Quality Standards | Electric                  
Air quality                  
Number of revisions necessary to meet the 2012 standard for particulate matter | performance_obligations         0        
Current number of micrograms per cubic meter that particulate matter needs to be below         12        
Current level of micrograms per cubic meter under 24-hour standard that fine particulate matter needs to be below         35        
National Ambient Air Quality Standards | Electric | Maximum                  
Air quality                  
Period of time for EPA Review of ozone plan 5 years                
Proposed primary (health-based) annual standard       10          
The EPA is taking comments on this full range of micrograms per cubic meter       11          
New possible number of micrograms per cubic meter that particulate matter may be lowered to       11          
Lowest limit that will cause nonattainment       10          
National Ambient Air Quality Standards | Electric | Minimum                  
Air quality                  
Period of time for EPA Review of ozone plan 3 years                
Proposed primary (health-based) annual standard       9          
The EPA is taking comments on this full range of micrograms per cubic meter       8          
New possible number of micrograms per cubic meter that particulate matter may be lowered to       10          
Climate Change | Electric                  
Air quality                  
Number of applicable GHG performance standards for coal plants | performance_obligations   0              
Percent capacity factor that if combined cycle natural gas plants are above it causes the rule to be highly dependent on hydrogen or carbon capture   50.00%              
Number of applicable limits that apply to simple cycle natural gas-fired combustion turbines that have less than a 20% capacity factor | performance_obligations   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%              
Rules that are being proposed for natural gas-fired stationary combustion turbines | performance_obligations   1              
Number of subcategories of stationary combustion turbine unit annual capacity factors that the proposed rule will be broken up into | performance_obligations   3              
Capacity of coal-fired generation retired, in megawatts | MW           1,900      
Capacity of fossil-fueled generation to be retired by the end of 2026, in megawatts | MW           1,500      
Company goal for percentage of carbon emissions reduction below 2005 levels by the end of 2025           60.00%      
Company goal for percentage of carbon emissions reduction below 2005 levels by the end of 2030           80.00%      
Climate Change | Electric | Maximum                  
Air quality                  
RICE Unit megawatts | MW   25              
Clean Water Act Cooling Water Intake Structure Rule | Electric                  
Water quality                  
Number of generating units that may be retired | generating_units           4      
Steam Electric Effluent Limitation Guidelines | Electric                  
Water quality                  
Number of new ELG rule requirements that affect our electric utilities | performance_obligations           2      
Capital investment to achieve required discharge limits | $           $ 105.0      
Steam Electric Effluent Limitation Guidelines | Electric | OCPP Units 7 and 8 | WE                  
Water quality                  
Capital investment to achieve required discharge limits | $                 $ 8.0
Steam Electric Effluent Limitation Guidelines | Electric | Weston Unit 3 | WPS                  
Water quality                  
Capital investment to achieve required discharge limits | $             $ 8.0    
Steam Electric Effluent Limitation Guidelines | Electric | Elm Road Generating Station | WE                  
Water quality                  
Capital investment to achieve required discharge limits | $           $ 89.0     $ 89.0
Percentage of completion of the ERGS biological treatment system           99.00%      
Manufactured Gas Plant Remediation | Natural gas                  
Manufactured gas plant remediation                  
Reserves for future environmental remediation | $           $ 456.6   499.6  
Manufactured Gas Plant Remediation | Natural gas | Environmental remediation costs                  
Manufactured gas plant remediation                  
Regulatory assets | $           $ 577.7   $ 610.7