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Regulatory Environment - COVID-19 (Details)
$ in Millions
1 Months Ended
Mar. 31, 2021
USD ($)
Jun. 30, 2020
USD ($)
Mar. 31, 2020
order
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Public Utilities, General Disclosures          
Regulatory asset       $ 3,306.9 $ 3,367.1
Public Service Commission of Wisconsin          
Public Utilities, General Disclosures          
Number of orders issued in response to COVID-19 | order     2    
Illinois Commerce Commission (ICC)          
Public Utilities, General Disclosures          
Additional period of time deposit requirements will be waived   4 months      
Percentage below federal poverty level for which customer disconnection is disallowed 300.00%        
Illinois Commerce Commission (ICC) | COVID-19          
Public Utilities, General Disclosures          
Recovery period of regulatory asset   36 months      
Regulatory asset       $ 9.5  
Illinois Commerce Commission (ICC) | PGL          
Public Utilities, General Disclosures          
Required funding to bill payment assistance program $ 6.0 $ 12.0      
Illinois Commerce Commission (ICC) | NSG          
Public Utilities, General Disclosures          
Required funding to bill payment assistance program $ 0.0 $ 1.2