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Regulatory Environment - MERC 2023 Rate Order (Details) - USD ($)
$ in Millions
1 Months Ended
Nov. 14, 2023
Dec. 31, 2022
Dec. 31, 2023
Public Utilities, General Disclosures      
Regulatory liability   $ 3,791.9 $ 3,745.2
Minnesota Public Utilities Commission (MPUC) | MERC      
Public Utilities, General Disclosures      
Interim rate increase   $ 37.0  
Approved rate increase $ 28.8    
Approved rate increase (as a percent) 7.10%    
Approved return on equity (as a percent) 9.65%    
Approved common equity component average (as a percent) 53.00%    
Minnesota Public Utilities Commission (MPUC) | MERC | Interim rate refunds      
Public Utilities, General Disclosures      
Regulatory liability     $ 8.5