XML 77 R54.htm IDEA: XBRL DOCUMENT v3.6.0.2
Regulatory Matters - Electric Rates (Details)
$ in Millions
12 Months Ended
Dec. 12, 2016
USD ($)
Nov. 02, 2016
USD ($)
Jun. 28, 2016
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Customers
Years
MW
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
PSCW [Member] | 2012 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Approved Return on Common Equity         10.90%    
PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Requested Rate Increase (Decrease)     3.10%        
Requested Return on Equity     10.90%        
Requested Equity Ratio     55.00%        
Annual Additional Revenue Generated from Requested Final Rate Increase     $ 2.7        
Electric Rates [Member] | MPUC [Member] | 2010 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [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 Customers [Member]              
Regulatory Matters [Line Items]              
Revenue from Cost Recovery Riders         $ 97.1 $ 89.6 $ 71.8
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Requested Rate Increase (Decrease)   9.00%          
Requested Return on Equity   10.25%          
Requested Equity Ratio   53.80%          
Annual Additional Revenue Generated from Requested Final Rate Increase   $ 55.0          
Annual Additional Revenue Generated from Requested Interim Rate Increase $ 34.7 49.0          
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Subsequent Event [Member]              
Regulatory Matters [Line Items]              
Annual Additional Revenue Generated from Requested Interim Rate Increase       $ 34.7      
Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Boswell Energy Center [Member]              
Regulatory Matters [Line Items]              
Expected Increase (Decrease) in Annual Depreciation Expense   $ (25.0)          
Electric Rates [Member] | MPUC [Member] | Renewable Cost Recovery Rider [Member] | Retail Customers [Member] | Corporate and Other [Member]              
Regulatory Matters [Line Items]              
After-Tax Change for North Dakota Investment Tax Credits Reversed         8.8    
Electric Rates [Member] | MPUC [Member] | Renewable Cost Recovery Rider [Member] | Minnesota Power [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Reduction in Operating Revenue due to Regulatory Outcome         15.0    
Electric Rates [Member] | MPUC [Member] | Annual Automatic Adjustment of Charges [Member] | Minnesota Power [Member] | Retail Customers [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    
Notice Required to Terminate (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] | 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 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 Contract (Termination Effective June 2019) [Member]              
Regulatory Matters [Line Items]              
Number of Customers | Customers         1    
Average Monthly Demand (MW) | MW         29    
Electric Rates [Member] | PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Requested Rate Increase (Decrease)     3.50%        
Natural Gas Rates [Member] | PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Requested Rate Increase (Decrease)     (1.30%)        
Water Rates [Member] | PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member]              
Regulatory Matters [Line Items]              
Requested Rate Increase (Decrease)     7.80%