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Property, Plant and Equipment | 12 Months Ended
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Dec. 31, 2014
Property, Plant and Equipment [Abstract] |
Property, Plant and Equipment [Text Block] | PROPERTY, PLANT AND EQUIPMENT
Property, Plant and Equipment |  |  |
As of December 31 | 2014 |  |  | 2013 |
Millions |  |  |
Regulated Utility |  | $3,903.3 |  |  |  | $3,380.0 |
Construction Work in Progress | 355.4 |  |  | 303.9 |
Accumulated Depreciation | (1,260.2 | ) |  | (1,181.7 | )
Regulated Utility Plant - Net | 2,998.5 |  |  | 2,502.2 |
Investments and Other Operations (a) | 357.8 |  |  | 131.3 |
Construction Work in Progress | 5.9 |  |  | 3.4 |
Accumulated Depreciation | (75.8 | ) |  | (60.4 | )
Investments and Other Operations Plant - Net | 287.9 |  |  | 74.3 |
Property, Plant and Equipment - Net |  | $3,286.4 |  |  |  | $2,576.5 |
(a) | Includes primarily ALLETE Clean Energy, BNI Coal and a small amount of non-rate base generation.
Depreciation is computed using the straight-line method over the estimated useful lives of the various classes of assets.
Estimated Useful Lives of Property, Plant and Equipment
Generation | 5 to 50 years |  | Distribution | 18 to 65 years
Transmission | 44 to 67 years |  | Investments and Other Operations | 5 to 44 years
Asset Retirement Obligations. We recognize, at fair value, obligations associated with the retirement of certain tangible, long-lived assets that result from the acquisition, construction, development or normal operation of the asset. Asset retirement obligations (ARO) relate primarily to the decommissioning of our coal-fired and wind generating facilities and land reclamation at BNI Coal, and are included in Other Non-Current Liabilities on our Consolidated Balance Sheet. The associated retirement costs are capitalized as part of the related long-lived asset and depreciated over the useful life of the asset. Removal costs associated with certain distribution and transmission assets have not been recognized, as these facilities have indeterminate useful lives. Conditional asset retirement obligations have been identified for treated wood poles and remaining polychlorinated biphenyl and asbestos-containing assets; however, removal costs have not been recognized because they are considered immaterial to our consolidated financial statements. Long-standing ratemaking practices approved by applicable state and federal regulatory commissions have allowed provisions for future plant removal costs in depreciation rates. These plant removal cost recoveries are classified either as AROs or as a regulatory liability for non-ARO obligations. To the extent annual accruals for plant removal costs differ from accruals under approved depreciation rates, a regulatory asset has been established in accordance with the guidance for AROs. (See Note 5. Regulatory Matters.)
Asset Retirement Obligation |  |
Millions |  |
Obligation as of December 31, 2012 |  |  | $77.9 |
Accretion |  | 4.6 |
Revisions in estimated cash flows |  | (0.7 | )
Obligation as of December 31, 2013 |  | 81.8 |
Accretion |  | 5.5 |
Liabilities recognized (a) |  | 23.0 |
Liabilities settled |  | (0.5 | )
Revisions in estimated cash flows |  | (0.6 | )
Obligation as of December 31, 2014 |  |  | $109.2 |
(a) | The increase in 2014 is primarily related to BNI Coal for coal mining expansion and ALLETE Clean Energy due to wind energy facilities acquisitions.

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- Definition The entire disclosure for long-lived, physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, accounting policies and methodology, roll forwards, depreciation, depletion and amortization expense, including composite depreciation, accumulated depreciation, depletion and amortization expense, useful lives and method used, income statement disclosures, assets held for sale and public utility disclosures. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2921-110230 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13-14) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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