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Operations and Significant Accounting Policies (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2015 | Dec. 31, 2014
Inventories [Abstract] |  |  |
Fuel |  | $ 54.0 | $ 29.0
Materials and Supplies |  | 52.6 | 51.5
Raw Materials |  | 3.1 | 0.0
Work in Progress |  | 0.7 | 0.0
Finished Goods |  | 8.9 | 0.0
Reserve for Obsolescence |  | (0.2) | 0.0
Total Inventories |  | 119.1 | 80.5
Prepayments and Other Current Assets [Abstract] |  |  |
Deferred Fuel Adjustment Clause |  | 16.3 | 16.3
Construction Costs for Development Project | [1] | 0.0 | 48.2
Restricted Cash | [2] | 8.1 | 2.7
Other |  | 18.1 | 14.8
Total Prepayments and Other Current Assets |  | 42.5 | 82.0
Other Current Liabilites [Abstract] |  |  |
Customer Deposits |  | 17.6 | 19.7
Power Purchase Agreements | [3] | 23.8 | 19.4
Construction Deposits Received for Development Project | [4] | 0.0 | 54.3
Billings in Excess of Costs and Estimated Earnings | [5] | 8.8 | 0.0
Other |  | 44.1 | 27.4
Total Other Current Liabilities |  | 94.3 | 120.8
Other Non-Current Liabilities [Abstract] |  |  |
Asset Retirement Obligation |  | 126.3 | 109.2
Power Purchase Agreements | [6] | 143.9 | 110.7
Contingent Consideration | [7] | 37.4 | 0.0
Other |  | 45.1 | 45.1
Total Other Non-Current Liabilities |  | 352.7 | 265.0
Debt Service and Other Requirements [Member] |  |  |
Restricted Cash, Noncurrent |  | $ 11.9 | $ 5.3
Minimum [Member] |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Definite-Lived Intangible Assets, Useful Life (Years) |  | 3 years |
Maximum [Member] |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Definite-Lived Intangible Assets, Useful Life (Years) |  | 22 years |
[1] | Construction Costs for Development Project relate to ALLETE Clean Energy’s project to develop and construct a wind energy facility in 2015. Beginning in the second quarter of 2015, these costs have been net against contract billings. (See Billings in Excess of Costs and Estimated Earnings in Other Current Liabilities table and Note 4. Acquisitions.)
[2] | Restricted Cash related to ALLETE Clean Energy’s wind energy facilities’ operating expense and capital distribution reserve requirements, and cash pledged as collateral by U.S. Water Services for stand-by letters of credit.
[3] | Power Purchase Agreements were acquired in conjunction with ALLETE Clean Energy’s wind energy facilities acquisitions. (See Note 4. Acquisitions.)
[4] | Construction Deposits Received for Development Project relate to ALLETE Clean Energy’s project to develop and construct a wind energy facility in 2015. Beginning in the second quarter of 2015, these deposits have been net against contract costs and estimated gross profit. (See Billings in Excess of Costs and Estimated Earnings below and Note 4. Acquisitions.)
[5] | Billings in Excess of Costs and Estimated Earnings represents the excess of contract billings over the construction costs incurred and estimated earnings recognized. In the second quarter of 2015, the NDPSC approved the sale agreement ALLETE Clean Energy has with Montana-Dakota Utilities to develop, construct, and sell a wind energy facility in 2015. (See Note 4. Acquisitions.)
[6] | Power Purchase Agreements were acquired in conjunction with ALLETE Clean Energy’s wind energy facilities acquisitions. (See Note 4. Acquisitions.)
[7] | Contingent Consideration relates to the estimated fair value of the earnings-based payment resulting from the U.S. Water Services acquisition. (See Note 4. Acquisitions and Note 6. Fair Value.)

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