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Regulatory Matters - Electric Rates (Details) - USD ($)
$ in Millions
3 Months Ended
Apr. 03, 2023
Feb. 28, 2023
Nov. 01, 2021
Mar. 31, 2023
Jun. 30, 2022
Mar. 31, 2022
Dec. 31, 2022
Regulatory Matters [Line Items]              
Regulatory Assets       $ 469.1     $ 441.0
MPUC [Member] | Minnesota Cost Recovery Riders [Member] | Minnesota Power [Member] | Retail Customers [Member] | Electric Rates [Member]              
Regulatory Matters [Line Items]              
Revenue from Cost Recovery Riders and Other Regulatory Programs       16.4   $ 6.5  
MPUC [Member] | 2022 Minnesota General Rate Review | Minnesota Power [Member] | Retail Customers [Member] | Electric Rates [Member]              
Regulatory Matters [Line Items]              
Revenue from Cost Recovery Riders and Other Regulatory Programs   $ 10.0          
Annual Additional Revenue Generated from Requested Final Rate Increase     $ 108.0        
Requested Rate Increase Percent     18.00%        
Requested Return on Equity     10.25%        
Requested Equity Capital Structure     53.81%        
Customer Refund Liability, Current       23.5     18.4
Approved Return on Common Equity   9.65%          
Public Utilities, Approved Equity Capital Structure, Percentage   52.50%          
Public Utilities, Approved Rate Increase (Decrease), Amount   $ 60.0          
MPUC [Member] | CIP Consolidated Filing Member | Minnesota Power [Member]              
Regulatory Matters [Line Items]              
Revenue from Cost Recovery Riders and Other Regulatory Programs         $ 1.9    
MPUC [Member] | CIP Consolidated Filing Member | Minnesota Power [Member] | Subsequent Event [Member]              
Regulatory Matters [Line Items]              
Revenue from Cost Recovery Riders and Other Regulatory Programs $ 2.2            
MPUC [Member] | Fuel Adjustment Clause 2022 | Minnesota Power [Member] | Electric Rates [Member]              
Regulatory Matters [Line Items]              
Regulatory Assets       $ 13.0     $ 13.0