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Regulatory Matters - Utility Rates (Details)
$ in Millions
6 Months Ended
Jun. 28, 2016
USD ($)
Jan. 01, 2013
Jun. 01, 2011
Jun. 30, 2016
USD ($)
Customers
Years
MW
Jun. 30, 2015
USD ($)
Minnesota Power [Member] | Bison Wind Energy Center [Member]          
Regulatory Matters [Line Items]          
Generating Capacity (MW) | MW       497  
PSCW [Member] | 2012 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Approved Return on Common Equity   10.90%      
PSCW [Member] | 2016 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Requested Rate Increase (Decrease) 3.10%        
Requested Return on Equity 10.90%        
Requested Equity Capital Structure 55.00%        
Requested Debt Capital Structure 45.00%        
Annual Additional Revenue Generated from Overall Requested Rate Increase | $ $ 2.7        
Electric Rates [Member] | MPUC [Member] | 2010 Minnesota Rate Case [Member] | Minnesota Power [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Approved Return on Common Equity     10.38%    
Approved Equity Ratio     54.29%    
Electric Rates [Member] | MPUC [Member] | Minnesota Cost Recovery Riders [Member] | Minnesota Power [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Revenue from Cost Recovery Riders | $       $ 48.9 $ 44.9
Electric Rates [Member] | MPUC [Member] | Renewable Cost Recovery Rider [Member] | Minnesota Power [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
North Dakota Investment Tax Credits | $       8.0  
Electric Rates [Member] | MPUC [Member] | Annual Automatic Adjustment of Charges [Member] | Minnesota Power [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Retail Fuel Cost Recovery Collected but Subject to Refund | $       $ 350.0  
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member]          
Regulatory Matters [Line Items]          
Number of Customers | Customers       16  
Length of Notice Required to Terminate Contract (Years) | Years       3  
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire December 2024) [Member]          
Regulatory Matters [Line Items]          
Number of Customers | Customers       14  
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire December 2024) [Member] | Maximum [Member]          
Regulatory Matters [Line Items]          
Change in Annual Capacity Charge Per Contract - Percentage       2.00%  
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire December 2024) [Member] | Minimum [Member]          
Regulatory Matters [Line Items]          
Change in Annual Capacity Charge Per Contract - Percentage       (1.00%)  
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Termination Effective June 2019) [Member]          
Regulatory Matters [Line Items]          
Number of Customers | Customers       1  
Average Monthly Demand (MW) | MW       29  
Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) [Member]          
Regulatory Matters [Line Items]          
Number of Customers | Customers       3  
Electric Rates [Member] | PSCW [Member] | 2016 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Requested Rate Increase (Decrease) 3.50%        
Natural Gas Rates [Member] | PSCW [Member] | 2016 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Requested Rate Increase (Decrease) (1.30%)        
Water Rates [Member] | PSCW [Member] | 2016 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail [Member]          
Regulatory Matters [Line Items]          
Requested Rate Increase (Decrease) 7.80%