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Regulatory Matters - Utility Rates (Details) (USD $) In Millions, unless otherwise specified | Sep. 30, 2014 Hydro Project [Member] | Sep. 30, 2014 Bison Wind Energy Center [Member] MW | Sep. 30, 2014 Bison 4 [Member] MW | Jun. 01, 2011 MPUC 2010 Minnesota Rate Case [Member] Electric Rates [Member] Retail Customers [Member] | Sep. 30, 2014 FERC-Approved Wholesale Rates [Member] Electric Rates [Member] Municipal Customers [Member] Years Customers | Dec. 31, 2012 PSCW 2012 Wisconsin Rate Case [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 |
Length of Notice Required to Terminate (in Years) |  |  |  |  | 3 |
Generating Capacity (MW) |  | 292 | 205 |  |  |
Estimated Capital Expenditures, Including Past Expenditures | $ 90 |  | $ 345 |  |  |
Capital Cost Spent to Date | $ 80 |  | $ 288 |  |  |

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- Details
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