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Property, Plant and Equipment | 12 Months Ended
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Dec. 31, 2018
Property, Plant and Equipment [Abstract] |
Property, Plant and Equipment [Text Block] | PROPERTY, PLANT AND EQUIPMENT
Property, Plant and Equipment |  |  |
As of December 31 | 2018 |  |  | 2017 |
Millions |  |  |
Regulated Operations |  |  |
Property, Plant and Equipment in Service |  | $4,490.6 |  |  |  | $4,523.7 |
Construction Work in Progress | 251.1 |  |  | 121.6 |
Accumulated Depreciation | (1,549.6 | ) |  | (1,520.5 | )
Regulated Operations – Net | 3,192.1 |  |  | 3,124.8 |
ALLETE Clean Energy |  |  |
Property, Plant and Equipment in Service | 488.4 |  |  | 482.5 |
Construction Work in Progress | 164.5 |  |  | 144.9 |
Accumulated Depreciation | (73.0 | ) |  | (60.8 | )
ALLETE Clean Energy – Net | 579.9 |  |  | 566.6 |
U.S. Water Services |  |  |
Property, Plant and Equipment in Service | 30.1 |  |  | 24.8 |
Accumulated Depreciation | (14.0 | ) |  | (10.4 | )
U.S. Water Services – Net | 16.1 |  |  | 14.4 |
Corporate and Other (a) |  |  |
Property, Plant and Equipment in Service | 214.3 |  |  | 204.7 |
Construction Work in Progress | 6.6 |  |  | 5.0 |
Accumulated Depreciation | (104.6 | ) |  | (93.1 | )
Corporate and Other – Net | 116.3 |  |  | 116.6 |
Property, Plant and Equipment – Net |  | $3,904.4 |  |  |  | $3,822.4 |
(a) | Primarily includes BNI Energy 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 (Years)
Regulated Operations |  |  | ALLETE Clean Energy | 5 to 35
Generation | 5 to 50 |  | U.S. Water Services | 5 to 39
Transmission | 52 to 71 |  | Corporate and Other | 3 to 50
Distribution | 19 to 68 |  |  |
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 (AROs) relate primarily to the decommissioning of our coal-fired and wind energy facilities, and land reclamation at BNI Energy. AROs are included in Other Non-Current Liabilities on the 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, the period of remediation is indeterminable and removal liabilities have not been recognized. Long-standing ratemaking practices approved by applicable state and federal regulatory authorities 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-AROs. 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 GAAP for AROs. (See Note 4. Regulatory Matters.) NOTE 2. PROPERTY, PLANT AND EQUIPMENT (Continued)
Asset Retirement Obligations |  |
Millions |  |
Obligation as of December 31, 2016 |  |  | $136.6 |
Accretion |  | 7.6 |
Liabilities Settled |  | (5.9 | )
Revisions in Estimated Cash Flows |  | (15.6 | )
Obligation as of December 31, 2017 |  | 122.7 |
Accretion |  | 7.0 |
Liabilities Settled |  | (5.3 | )
Revisions in Estimated Cash Flows |  | 14.2 |
Obligation as of December 31, 2018 |  |  | $138.6 |

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -URI http://asc.fasb.org/topic&trid=2155823 + Details
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