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Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  |  |  |  |  | 3 Months Ended |  |
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Sep. 30, 2011 | Dec. 31, 2010 | May 24, 2011 2010 Rate Case [Member] | Mar. 31, 2011 2010 Rate Case [Member] | Dec. 31, 2010 2010 Rate Case [Member] | Nov. 02, 2010 2010 Rate Case [Member] Percent | Apr. 30, 2010 2010 Rate Case [Member] Percent | Nov. 02, 2009 2010 Rate Case [Member] | Sep. 30, 2011 FERC-Approved Wholesale Rates [Member] | Sep. 30, 2011 2010 Wisconsin Rate Increase [Member] | Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Percent | Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Water Rates [Member] Percent | Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Natural Gas Rates [Member] Percent | Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Electric Rates [Member] Percent | Mar. 31, 2011 DTL Reversal, Revenue Receivable Forgone [Member] | Jun. 30, 2011 Income Tax Benefit, MPUC Approval of Deferral of PPACA [Member] | Mar. 31, 2010 DTA Reversal, Elimination of Medicare Part D [Member] | Sep. 30, 2011 Medicare Part D [Member] | Dec. 31, 2010 Medicare Part D [Member]
Electric Rates [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Original Retail Rate Increase Request |  |  |  |  |  |  |  | $ 81 |  |  |  |  |  |  |  |  |  |  |
Interim Rate Increase Implemented |  |  |  |  | 48.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Adjusted Retail Rate Increase Request |  |  |  |  |  |  | 72 |  |  |  |  |  |  |  |  |  |  |  |
Requested Rate of Return on Common Equity |  |  |  |  |  |  | 11.25% |  |  |  |  |  |  |  |  |  |  |  |
Requested Percentage of Capital Structure Related to Equity |  |  |  |  |  |  | 54.29% |  |  |  |  |  |  |  |  |  |  |  |
Requested Percentage of Capital Structure Related to Debt |  |  |  |  |  |  | 45.71% |  |  |  |  |  |  |  |  |  |  |  |
Approved Retail Rate Increase |  |  | 53.5 |  |  | 53.5 |  |  |  |  |  |  |  |  |  |  |  |  |
Approved Rate of Return on Common Equity |  |  |  |  |  | 10.38% |  |  |  |  | 10.90% |  |  |  |  |  |  |  |
Approved Percentage of Capital Structure Related to Equity |  |  |  |  |  | 54.29% |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of Rate Differential Authorized for Collection |  |  | 3.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of Revenue Receivable Capitalized |  |  |  | 20.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Adjustments, Settlements, and Unusual Provisions |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.2 | 2.9 | 4.0 |  |
Non-Affiliated Municipal Customers, Municipalities |  |  |  |  |  |  |  |  | 16 |  |  |  |  |  |  |  |  |  |
Non-Affiliated Municipal Customers, Private Utilities |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Length of Notice Required to Terminate (Years) |  |  |  |  |  |  |  |  | three |  |  |  |  |  |  |  |  |  |
Amount Of Estimated Additional Revenue |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Approved Retail Rate Increase (Percent) |  |  |  |  |  |  |  |  |  |  | 2.40% | 12.80% | 2.50% | 0.70% |  |  |  |  |
The Patient Protection and Affordable Care Act of 2010 (PPACA) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Adjustments, Settlements, and Unusual Provisions |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.2 | 2.9 | 4.0 |  |
Non-Current Regulatory Assets | $ 286.9 | $ 310.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5.0 | $ 0

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- Definition The entity's adjusted requested amount of increase to existing rates, filed with the state regulatory commission. + Details
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- Definition The amount of estimated additional revenue generated on an annualized basis as a result of a rate increase. + Details
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- Definition The amount of differential between interim rates and final rates authorized for collection by the state regulatory commission through a rate case proceeding. + Details
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- Definition Percentage of capital structure related to equity approved by the state regulatory commission through a rate case proceeding. + Details
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- Definition Rate of return on common equity approved by the state regulatory commission through a rate case proceeding. + Details
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- Definition The entity's approved amount of increase to electric rates, by the state regulatory commission. + Details
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- Definition The entity's approved rate of increase to existing rates, by the state regulatory commission. + Details
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- Definition The length of notice required to terminate a contract in years. + Details
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- Definition The entity's original requested amount of increase to existing rates, filed with the state regulatory commission. + Details
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- Definition Percentage of capital structure related to debt requested by utility through a rate case proceeding filed with the state regulatory commission. + Details
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- Definition Rate of return on common equity requested by utility through a rate case proceeding filed with the state regulatory commission. + Details
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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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- Definition Reflects the effects of adjustments of previously recorded tax expense, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, IRS tax settlement and unusual repatriation of foreign earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 48 -Paragraph 10 -Subparagraph b -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 FASB Interpretation (FIN) -Number 48 -Paragraph 10A, 10B, 10C -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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