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Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  | 3 Months Ended |  | 3 Months Ended |  |  |  |  |
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Mar. 31, 2012 | Dec. 31, 2011 | Mar. 31, 2012 Medicare Part D [Member] | Dec. 31, 2011 Medicare Part D [Member] | Jun. 30, 2011 Income Tax Benefit, MPUC Approval of Deferral of PPACA [Member] | Mar. 31, 2012 Income Tax Benefit, MPUC Approval of Deferral of PPACA [Member] Medicare Part D [Member] | Mar. 31, 2010 DTA Reversal, Elimination of Medicare Part D [Member] | Jun. 01, 2011 2010 MN Rate Case [Member] | Mar. 31, 2012 FERC-Approved Wholesale Rates [Member] Customers | Jun. 01, 2011 FERC-Approved Wholesale Rates [Member] | Mar. 31, 2012 Non-Affiliated Municipal Customers, Private Utilities [Member] | Dec. 31, 2010 2010 Wisconsin Rate Increase [Member]
Electric Rates [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Approved Rate of Return on Common Equity |  |  |  |  |  |  |  |  |  | 10.38% |  | 10.90%
Approved Percentage of Capital Structure Related to Equity |  |  |  |  |  |  |  | 54.29% |  |  |  |
Tax Adjustments, Settlements, and Unusual Provisions |  |  |  |  | $ 2.9 |  | $ 4.0 |  |  |  |  |
Non-Affiliated Municipal Customers, Municipalities |  |  |  |  |  |  |  |  | 16 |  |  |
Non-Affiliated Municipal Customers, Private Utilities |  |  |  |  |  |  |  |  | 1 |  |  |
Length of Notice Required to Terminate (Years) |  |  |  |  |  |  |  |  | 3 |  | 2 |
The Patient Protection and Affordable Care Act of 2010 (PPACA) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Tax Adjustments, Settlements, and Unusual Provisions |  |  |  |  | 2.9 |  | 4.0 |  |  |  |  |
Non-Current Regulatory Assets | $ 339.3 | $ 345.9 | $ 5.0 | $ 5.0 |  | $ 5.0 |  |  |  |  |  |

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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 9, 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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