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Regulatory Matters - Electric Rates (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2013 Bison Wind Energy Center [Member] MW | Jun. 01, 2011 MPUC 2010 Minnesota Rate Case [Member] Electric Rates [Member] Retail Customers [Member] | Mar. 31, 2013 FERC-Approved Wholesale Rates [Member] Electric Rates [Member] Municipal Customers [Member] Years Customers | Mar. 31, 2013 FERC-Approved Wholesale Rates [Member] Electric Rates [Member] Non-Affiliated Private Utility [Member] Years Customers | Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Retail Customers [Member] | Dec. 31, 2012 PSCW 2012 Wisconsin Rate Case [Member] Retail Customers [Member] | Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Electric Rates [Member] Retail Customers [Member] | Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Natural Gas Rates [Member] Retail Customers [Member] | Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Water Rates [Member] Retail Customers [Member]
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Rate Regulation [Line Items] |  |  |  |  |  |  |  |  |
Approved Rate of Return on Common Equity |  | 10.38% |  |  |  | 10.90% |  |  |
Approved Percentage of Capital Structure Related to Equity |  | 54.29% |  |  |  |  |  |  |
Number of Customers |  |  | 16 | 1 |  |  |  |  |
Length of Notice Required to Terminate (in Years) |  |  | 3 | 2 |  |  |  |  |
Approved Rate Increase or Decrease |  |  |  |  | 2.40% |  | 1.20% | (0.20%) | 13.80%
Amount Of Estimated Additional Revenue |  |  |  |  | $ 1.7 |  |  |  |
Generating Capacity (MW) | 292 |  |  |  |  |  |  |  |

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- Details
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