Document and Entity Information Document |
6 Months Ended |
|---|---|
|
Jun. 30, 2018
shares
| |
| Document and Entity Information [Line Items] | |
| Entity Registrant Name | ALLETE INC |
| Entity Central Index Key | 0000066756 |
| Entity Tax Identification Number | 410418150 |
| Current Fiscal Year End Date | --12-31 |
| Entity Well-known Seasoned Issuer | Yes |
| Entity Voluntary Filers | No |
| Entity Current Reporting Status | Yes |
| Entity Filer Category | Large Accelerated Filer |
| Entity Common Stock, Shares Outstanding | 51,360,616 |
| Document Fiscal Year Focus | 2018 |
| Document Fiscal Period Focus | Q2 |
| Document Type | 10-Q |
| Amendment Flag | false |
| Document Period End Date | Jun. 30, 2018 |
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- Definition If the value is true, then the document is an amendment to previously-filed/accepted document. No definition available.
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- Definition End date of current fiscal year in the format --MM-DD. No definition available.
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- Definition This is focus fiscal period of the document report. For a first quarter 2006 quarterly report, which may also provide financial information from prior periods, the first fiscal quarter should be given as the fiscal period focus. Values: FY, Q1, Q2, Q3, Q4, H1, H2, M9, T1, T2, T3, M8, CY. No definition available.
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- Definition This is focus fiscal year of the document report in CCYY format. For a 2006 annual report, which may also provide financial information from prior periods, fiscal 2006 should be given as the fiscal year focus. Example: 2006. No definition available.
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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- Definition The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD. No definition available.
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- Definition The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'. No definition available.
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- Definition A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Indicate number of shares or other units outstanding of each of registrant's classes of capital or common stock or other ownership interests, if and as stated on cover of related periodic report. Where multiple classes or units exist define each class/interest by adding class of stock items such as Common Class A [Member], Common Class B [Member] or Partnership Interest [Member] onto the Instrument [Domain] of the Entity Listings, Instrument. No definition available.
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- Definition Indicate 'Yes' or 'No' whether registrants (1) have filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that registrants were required to file such reports), and (2) have been subject to such filing requirements for the past 90 days. This information should be based on the registrant's current or most recent filing containing the related disclosure. No definition available.
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- Definition Indicate whether the registrant is one of the following: (1) Large Accelerated Filer, (2) Accelerated Filer, (3) Non-accelerated Filer, (4) Smaller Reporting Company (Non-accelerated), (5) Smaller Reporting Accelerated Filer or (6) Smaller Reporting Company and Large Accelerated Filer. Definitions of these categories are stated in Rule 12b-2 of the Exchange Act. This information should be based on the registrant's current or most recent filing containing the related disclosure. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Indicate 'Yes' or 'No' if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. No definition available.
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- Definition Indicate 'Yes' or 'No' if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Is used on Form Type: 10-K, 10-Q, 8-K, 20-F, 6-K, 10-K/A, 10-Q/A, 20-F/A, 6-K/A, N-CSR, N-Q, N-1A. No definition available.
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| X | ||||||||||
- Definition Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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| X | ||||||||||
- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Represents the caption on the face of the balance sheet to indicate that the entity has entered into (1) purchase or supply arrangements that will require expending a portion of its resources to meet the terms thereof, and (2) is exposed to potential losses or, less frequently, gains, arising from (a) possible claims against a company's resources due to future performance under contract terms, and (b) possible losses or likely gains from uncertainties that will ultimately be resolved when one or more future events that are deemed likely to occur do occur or fail to occur. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Aggregate par or stated value of issued nonredeemable common stock (or common stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable common shares, par value and other disclosure concepts are in another section within stockholders' equity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences, with jurisdictional netting and classified as noncurrent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance. No definition available.
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| X | ||||||||||
- Definition Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of liabilities and equity items, including the portion of equity attributable to noncontrolling interests, if any. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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| X | ||||||||||
- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of current assets classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of noncurrent assets classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The cumulative amount of the reporting entity's undistributed earnings or deficit. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition Carrying value as of the balance sheet date of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Consolidated Balance Sheet Parentheticals - USD ($) shares in Millions, $ in Millions |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Accounts Receivable [Abstract] | ||
| Accounts Receivable, Allowance | $ 2.3 | $ 2.1 |
| Common Stock [Abstract] | ||
| Common Stock, Par Value | $ 0.00 | $ 0.00 |
| Common Stock, Shares Authorized | 80.0 | 80.0 |
| Common Stock, Shares Outstanding | 51.4 | 51.1 |
| Common Stock, Shares Issued | 51.4 | 51.1 |
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- References No definition available.
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- Definition A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Face amount per share of no-par value common stock. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition The maximum number of common shares permitted to be issued by an entity's charter and bylaws. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The amount of income recognized in the current period that reflects income associated with the reduced liability of the PPAs acquired in a business acquisition. As noncash income, this element is subtracted from net income when calculating cash provided by or used in operations using the indirect method. No definition available.
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- Definition Fuel, Purchased Power and Gas - Utility No definition available.
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- Definition Transmission Services - Utility No definition available.
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Total costs of sales and operating expenses for the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References No definition available.
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| X | ||||||||||
- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of the cost of borrowed funds accounted for as interest expense. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense. No definition available.
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| X | ||||||||||
- Definition The net result for the period of deducting operating expenses from operating revenues. No definition available.
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| X | ||||||||||
- Definition Amount of income (expense) related to nonoperating activities, classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The total amount of regulated operating revenues recognized during the period. No definition available.
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| X | ||||||||||
- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of tax expense classified as other. No definition available.
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| X | ||||||||||
- Definition The amount of unregulated operating revenues recognized during the period. No definition available.
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| X | ||||||||||
- Definition The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Consolidated Statement of Comprehensive Income - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Comprehensive Income [Abstract] | ||||
| Net Income | $ 31.3 | $ 36.9 | $ 82.3 | $ 85.9 |
| Other Comprehensive Income (Loss) [Abstract] | ||||
| Currency Translation Adjustments | 0.0 | (0.2) | 0.0 | (0.2) |
| Unrealized Gain (Loss) on Securities Net of Income Tax Expense of $–, $0.2, $– and $0.5 | 0.0 | 0.4 | (0.1) | 0.7 |
| Defined Benefit Pension and Other Postretirement Benefit Plans Net of Income Tax Expense of $0.1, $0.2, $0.2 and $0.3 | 0.3 | 0.2 | 0.7 | 0.4 |
| Total Other Comprehensive Income | 0.3 | 0.4 | 0.6 | 0.9 |
| Total Comprehensive Income | $ 31.6 | $ 37.3 | $ 82.9 | $ 86.8 |
| X | ||||||||||
- Definition Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after tax and reclassification adjustments of other comprehensive income (loss). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Consolidated Statement of Comprehensive Income Parentheticals - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Statement of Comprehensive Income [Abstract] | ||||
| Unrealized Gain (Loss) on Securities, Income Tax Expense | $ 0.0 | $ 0.2 | $ 0.0 | $ 0.5 |
| Defined Benefit Pension and Other Postretirement Benefit Plans, Income Tax Expense | $ 0.1 | $ 0.2 | $ 0.2 | $ 0.3 |
| X | ||||||||||
- Definition Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income of defined benefit plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition The amount of income recognized in the current period that reflects income associated with the reduced liability of the PPAs acquired in a business acquisition. As noncash income, this element is subtracted from net income when calculating cash provided by or used in operations using the indirect method. No definition available.
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| X | ||||||||||
- Definition Provision for Interim Rate Refund No definition available.
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| X | ||||||||||
- Definition Provision for Tax Reform Refund No definition available.
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| X | ||||||||||
- Definition Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of increase (decrease) in cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage; excluding effect from exchange rate change. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition This element represents the undistributed income (or loss) of equity method investments, net of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporations; such investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the amount due from customers for the credit sale of goods and services; includes accounts receivable and other types of receivables. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the aggregate amount of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the capitalized cost of equity (based on assumed rate of return) and / or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. As a result of this capitalization, net income is increased. This element pertains to certain regulated industries, such as public utilities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of increase (decrease) in current liabilities classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of increase (decrease) in noncurrent assets classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of increase (decrease) in noncurrent operating liabilities classified as other. No definition available.
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| X | ||||||||||
- Definition Amount of increase (decrease) in prepaid expenses, and assets classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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- Definition Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- References No definition available.
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| X | ||||||||||
- Definition Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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| X | ||||||||||
- Definition Amount of expense charged against earnings to allocate the cost of tangible and intangible assets over their remaining economic lives, classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of cash outflow, not made soon after acquisition date of business combination, to settle contingent consideration liability up to amount recognized at acquisition date, including, but not limited to, measurement period adjustment and less amount paid soon after acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The cash outflow to acquire debt and equity securities not classified as either held-to-maturity securities or trading securities which would be classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cost (reversal of cost) for pension and other postretirement benefits. No definition available.
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| X | ||||||||||
- Definition Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The cash inflow from the additional capital contribution to the entity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cash inflow (outflow) from financing activities classified as other. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cash inflow from the sale of other assets recognized in investing activities. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of expense related to write-down of receivables to the amount expected to be collected. Includes, but is not limited to, accounts receivable and notes receivable. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Consolidated Statement of Shareholders' Equity - USD ($) $ in Millions |
Total |
Retained Earnings [Member] |
Accumulated Other Comprehensive Loss [Member] |
Common Stock [Member] |
||
|---|---|---|---|---|---|---|
| Consolidated Statement of Shareholders' Equity [Roll Forward] | ||||||
| Adjustments to Opening Balances - Net of Income Taxes | [1] | $ 0.5 | $ 6.1 | $ (5.6) | $ 0.0 | |
| Beginning Balance - Adjusted | 2,068.7 | 695.5 | (28.2) | 1,401.4 | ||
| Beginning Balance at Dec. 31, 2017 | 2,068.2 | 689.4 | (22.6) | 1,401.4 | ||
| Comprehensive Income [Abstract] | ||||||
| Net Income | 82.3 | 82.3 | ||||
| Other Comprehensive Income – Net of Tax [Abstract] | ||||||
| Unrealized Loss on Debt Securities | (0.1) | (0.1) | ||||
| Defined Benefit Pension and Other Postretirement Plans | 0.7 | 0.7 | ||||
| Total Comprehensive Income | 82.9 | |||||
| Common Stock Issued | 14.0 | 14.0 | ||||
| Dividends Declared | (57.4) | (57.4) | ||||
| Ending Balance at Jun. 30, 2018 | $ 2,108.2 | $ 720.4 | $ (27.6) | $ 1,415.4 | ||
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- Definition Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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| X | ||||||||||
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. No definition available.
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- Definition Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
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- References No definition available.
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| X | ||||||||||
- Definition Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of stockholders' equity including the portion attributable to noncontrolling interests, after the cumulative effect adjustment of a new accounting principle applied in the period of adoption. No definition available.
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Operations and Significant Accounting Policies |
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| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Operations and Significant Accounting Policies [Text Block] | OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES Cash, Cash Equivalents and Restricted Cash. We consider all investments purchased with original maturities of three months or less to be cash equivalents. Restricted cash amounts included in Prepayments and Other on the Consolidated Balance Sheet include collateral deposits required under an ALLETE Clean Energy loan agreement and U.S. Water Service’s standby letters of credit. The restricted cash amounts included in Other Non-Current Assets represent collateral deposits required under an ALLETE Clean Energy loan agreement and PSAs, and deposits from a SWL&P customer in aid of future capital expenditures. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheet that aggregate to the amount presented in the Consolidated Statement of Cash Flows. During the first quarter of 2018, the Company updated the presentation of its Consolidated Statement of Cash Flows to include restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the Consolidated Statement of Cash Flows. (See Recently Adopted Pronouncements - Statement of Cash Flows: Restricted Cash.)
Inventories – Net. Inventories are stated at the lower of cost or net realizable value. Inventories in our Regulated Operations segment are carried at an average cost or first-in, first-out basis. Inventories in our U.S. Water Services and ALLETE Clean Energy segments, and Corporate and Other businesses are carried at an average cost, first-in, first-out or specific identification basis.
NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued)
NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Supplemental Statement of Cash Flows Information.
Subsequent Events. The Company performed an evaluation of subsequent events for potential recognition and disclosure through the date of the financial statements issuance. Revenue. Contracts with Customers – Utility includes sales from our regulated operations for generation, transmission and distribution of electric service, and distribution of water and gas services to our customers. Also included is an immaterial amount of regulated steam generation that is used by customers in the production of paper and pulp. Contracts with Customers – Non-utility includes sales of goods and services to customers from ALLETE Clean Energy, U.S. Water Services and our Corporate and Other businesses. Other – Non-utility is the non-cash adjustments to revenue recognized by ALLETE Clean Energy for the amortization of differences between contract prices and estimated market prices for PSAs that were assumed during the acquisition of various wind energy facilities. Revenue Recognition Revenue is recognized upon transfer of control of promised goods or services to our customers in an amount that reflects the consideration we expect to receive in exchange for those products or services. Revenue is recognized net of allowance for returns and any taxes collected from customers, which are subsequently remitted to the appropriate governmental authorities. We account for shipping and handling activities that occur after the customer obtains control of goods as a cost rather than an additional performance obligation thereby recognizing revenue at time of shipment and accruing shipping and handling costs when control transfers to our customers. We have a right to consideration from our customers in an amount that corresponds directly with the value to the customer for our performance completed to date; therefore, we may recognize revenue in the amount to which we have a right to invoice. Nature of Revenue Streams Utility Residential and Commercial includes sales for electric, gas or water service to customers, who have implied contracts with the utility, under rates governed by the MPUC, PSCW or FERC. Customers are billed on a monthly cycle basis and revenue is recognized for electric, gas or water service delivered during the billing period. Revenue is accrued for service provided but not yet billed at period end. Performance obligations with these customers are satisfied at time of delivery to customer meters and simultaneously consumed. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Revenue (Continued) Municipal includes sales to 16 non-affiliated municipal customers in Minnesota under long-term wholesale electric contracts. All wholesale electric contracts include a termination clause requiring a three-year notice to terminate. These contracts have termination dates ranging from 2019 through at least 2032, with a majority of contracts effective through at least 2024. Performance obligations with these customers are satisfied at the time energy is delivered to an agreed upon municipal substation or meter. Industrial includes sales recognized from contracts with customers in the taconite mining, iron concentrate, paper, pulp and secondary wood products, pipeline and other industries. Industrial sales accounted for approximately 49 percent of total regulated utility kWh sales for the six months ended June 30, 2018. Within industrial revenue, Minnesota Power has 9 Large Power Customer contracts, each serving requirements of 10 MW or more of customer load. These contracts automatically renew past the contract term unless a four-year advanced written notice is given. Large Power Customer contracts have earliest termination dates ranging from 2022 through 2026. We satisfy our performance obligations for these customers at the time energy is delivered to an agreed upon customer substation. Revenue is accrued for energy provided but not yet billed at period end. Based on current contracts with industrial customers, we expect to recognize minimum revenue for the fixed contract components of approximately $70 million per annum through 2019, $50 million in 2020 and 2021, $30 million in 2022 and $30 million for aggregate years thereafter, which reflects the termination notice period in these contracts. When determining minimum revenue, we assume that customer contracts will continue under the contract renewal provision; however, if long-term contracts are renegotiated and subsequently approved by the MPUC or there are changes within our industrial customer class, these amounts may be impacted. Contracts with customers that contain variable pricing or quantity components are excluded from the expected minimum revenue amounts. Other Power Suppliers includes the sale of energy under long-term PSAs with two customers as well as MISO market and liquidation sales. Expiration dates of these PSAs range from 2020 through 2026. Performance obligations with these customers are satisfied at the time energy is delivered to an agreed upon delivery point defined in the contract (generally the MISO pricing node). Based on current contracts with two customers, we expect to recognize minimum revenue for fixed contract components of approximately $10 million per annum through 2019. Other power supplier contracts that extend beyond 2020 contain variable pricing components that prevent us from estimating future minimum revenue, and therefore are not included. Other Revenue includes all remaining individually immaterial revenue streams for Minnesota Power and SWL&P, and is comprised of steam sales to paper and pulp mills, wheeling revenue and other sources. Revenue for steam sales to customers is recognized at the time steam is delivered and simultaneously consumed. Revenue is recognized at the time each performance obligation is satisfied. Alternative Programs includes revenue that is driven by factors outside of our regulated entities’ control or as a result of the achievement of certain objectives, such as CIP financial incentives. This revenue is accounted for in accordance with the accounting standards for alternative revenue programs which allow for the recognition of revenue under an alternative revenue program if the program is established by an order from the utility’s regulatory commission, the order allows for automatic adjustment of future rates, the amount of revenue recognized is objectively determinable and probable of recovery, and the revenue will be collected within 24 months following the end of the annual period in which it is recognized. CIP financial incentives are recognized in the period in which the MPUC approves the filing, which is typically mid-year. Non-utility ALLETE Clean Energy Long-term PSA revenue includes all sales recognized under long-term contracts for production, curtailment, capacity and associated renewable energy credits from ALLETE Clean Energy wind energy facilities. Expiration dates of these PSAs range from 2018 through 2032. Performance obligations for these contracts are satisfied at the time energy is delivered to an agreed upon point, or production is curtailed at the request of the customer, at specified prices. Revenue from the sale of renewable energy credits is recognized at the same time the related energy is delivered to the customer when sold to the same party. Other is the non-cash adjustments to revenue recognized by ALLETE Clean Energy for the amortization of differences between contract prices and estimated market prices on assumed PSAs. As part of wind energy facility acquisitions, ALLETE Clean Energy assumed various PSAs that were above or below estimated market prices at the time of acquisition; the resulting differences between contract prices and estimated market prices are amortized to revenue over the remaining PSA term. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Revenue (Continued) U.S. Water Services Point-in-time revenue is recognized for purchases by customers for chemicals, consumable equipment (e.g. filters, pumps and valves) or related maintenance and repair services as the customer’s usage and needs change over time. These goods and services are purchased on an as-needed basis by the customers and therefore revenue can be variable. Products are shipped to the customer in accordance with the terms of the purchase order, and performance obligations are satisfied at the time of shipment of goods or when services are rendered to the customer. Contract includes monthly revenue from contracts with customers to provide chemicals, consumable equipment and services to meet customer needs during the contract period. As agreed with the customer, a fixed amount is invoiced based on the goods and services to be provided under the contract. The duration of these contracts generally range in length from three months to five years and automatically renew. A 30-day notice is required to terminate such contracts without penalty after contract execution. Performance obligations are satisfied during the period as goods and service are delivered in accordance with the terms of the contract. Capital Project includes the sale of equipment and other components assembled to create a water treatment system for the customer. These projects are provided under contracts at an agreed upon price to meet a customer's specifications and typically take less than one year to complete. In general, progress payments are received throughout the project period and are recorded as contract liabilities until performance obligations are satisfied at the time the equipment and other components are delivered to the customer’s site. Corporate and Other Long-term Contract encompasses the sale and delivery of coal to customer generation facilities. Revenue is recognized on a monthly basis at the cost of production plus a specified profit per ton of coal delivered to the customer. Coal sales are secured under long-term coal supply agreements extending through 2037. Performance obligations are satisfied during the period as coal is delivered to customer generation facilities. Other primarily includes revenue from BNI Energy unrelated to coal, the sale of real estate from ALLETE Properties, and non‑rate base steam generation that is sold for use during production of paper and pulp. Performance obligations are satisfied when control transfers to the customer. Payment Terms Payment terms and conditions vary across our businesses. Aside from taconite-producing Large Power Customers, payment terms generally require payment to be made within 15 to 30 days from the end of the period that the service has been rendered or goods provided. In the case of its taconite-producing Large Power Customers, as permitted by the MPUC, Minnesota Power requires weekly payments for electric usage based on monthly energy usage estimates. These customers receive estimated bills based on Minnesota Power’s estimate of the customers’ energy usage, forecasted energy prices and fuel adjustment clause estimates. Minnesota Power’s taconite-producing Large Power Customers have generally predictable energy usage on a weekly basis and any differences that occur are trued-up the following month. Due to the timing difference of revenue recognition from the timing of invoicing and payment, the customer receives credit for the time value of money; however, we have determined that our contracts do not include a significant financing component as the period between when we transfer the service to the customer and when they pay for such service is minimal. Assets Recognized From the Costs to Obtain a Contract with a Customer We recognize as an asset the incremental costs of obtaining a contract with a customer if we expect the benefit of those costs to be longer than one year. We expense incremental costs when the asset that would have resulted from capitalizing these costs would have been amortized in one year or less. As of June 30, 2018, we have $30.9 million of assets recognized for costs incurred to obtain contracts with our customers ($31.6 million as of December 31, 2017). Management determined the amount of costs to be recognized as assets based on actual costs incurred and paid to obtain and fulfill these contracts to provide goods and services to our customers. Assets recognized to obtain contracts are amortized on a straight-line basis over the contract term as a non-cash reduction to revenue. For the six months ended June 30, 2018, and 2017, we recognized $1.3 million of non-cash amortization. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) New Accounting Pronouncements. Recently Adopted Pronouncements Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. In February 2018, the FASB issued an update allowing for a one-time reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the enactment of the TCJA. With the enactment of the new federal tax rates in 2017, entities were required to adjust deferred tax assets and liabilities to reflect the lower federal rate with the effect of this reduction impacting income from continuing operations in the period of enactment, even in instances where the related income tax effects of items were originally recognized in other comprehensive income. As such, companies were left with stranded tax effects in accumulated other comprehensive income that did not reflect the appropriate tax rate. This guidance is effective in the first quarter of 2019 with early adoption permitted. The Company elected to early adopt this guidance in the first quarter of 2018 which resulted in a reduction of $5.7 million to Accumulated Other Comprehensive Loss and a corresponding increase to Retained Earnings for the reclassification of the stranded income tax effects. Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. In March 2017, the FASB issued an accounting standard update to improve the presentation of net periodic pension and postretirement benefit costs. Under the guidance, an entity is required to present the service cost component of the net periodic benefit cost in the same income statement line as other employee compensation costs arising from services rendered during the period. The guidance also allows only the service cost component of the periodic cost to be eligible for capitalization on a prospective basis. The other components of net periodic expense must be presented separately from the line item that includes the service cost and must be excluded from the operating income subtotal. The Company adopted the guidance in the first quarter of 2018 and retrospectively adjusted the presentation of the service cost component and the other components of net periodic costs in the Consolidated Statement of Income. The retrospective adjustments for the quarter and six months ended June 30, 2017, were as follows: Operating and Maintenance increased $1.0 million and $2.1 million, respectively, Cost of Sales – Non-utility remained unchanged and decreased $0.1 million, respectively, resulting in an increase of $1.0 million and $2.0 million, respectively to Other Income (Expense) – Other. There was no impact to net income as a result of adoption. Financial Instruments. In 2016, the FASB issued an accounting standard update which requires entities to measure equity investments at fair value and recognize any changes in fair value in net income unless the investments qualify for the practicability exception. The practicability exception will be available for equity investments that do not have readily determinable fair values. The update was adopted by the Company in the first quarter of 2018 which resulted in a cumulative-effect transition adjustment reducing Retained Earnings by $0.1 million, including the tax effect, for the previously unrealized loss on available-for-sale equity securities in Accumulated Other Comprehensive Loss as of December 31, 2017. Classification of Certain Cash Receipts and Cash Payments. In 2016, the FASB issued an accounting standard update which addressed the following eight specific cash flow issues: debt prepayment or debt extinguishment costs; settlement of zero‑coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies (including bank-owned life insurance policies); distributions received from equity method investees; beneficial interests in securitization transactions; and separately identifiable cash flows and application of the predominance principle. The amendments of this update were adopted by the Company in the first quarter of 2018. There was no impact to the Consolidated Statement of Cash Flows as a result of adoption. Statement of Cash Flows: Restricted Cash. In 2016, the FASB issued an accounting standard update related to the presentation of restricted cash in the Company’s Consolidated Statement of Cash Flows. The update requires that the Consolidated Statement of Cash Flows explain the change during the period in cash, cash equivalents and restricted cash. Restricted cash should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the Consolidated Statement of Cash Flows. This guidance update was adopted by the Company in the first quarter of 2018 and was applied retrospectively to the periods presented in the Consolidated Statement of Cash Flows which resulted in a net increase in cash from financing activities of $1.5 million for the six months ended June 30, 2017. Additional disclosure, including a reconciliation of the beginning-of-period and end-of-period cash on hand to the statement of cash flows, is included in this note. (See Cash, Cash Equivalents and Restricted Cash.) NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) New Accounting Pronouncements (Continued) Revenue from Contracts with Customers. In 2014, the FASB issued amended revenue recognition guidance that clarifies the principles for recognizing revenue from contracts with customers by providing a single comprehensive model to determine the measurement of revenue and timing of recognition. The guidance requires an entity to recognize revenue in a manner that depicts the transfer of goods or services to customers in an amount that reflects the consideration to which an entity expects to be entitled to in exchange for those goods or services. The guidance requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures regarding customer contracts, significant judgments and changes in those judgments, and the assets recognized from the costs to obtain or fulfill a contract are required. The Company adopted this accounting guidance in the first quarter of 2018 and elected to apply the modified retrospective method of adoption to all contracts as of the date of initial application. The financial impact to the consolidated financial statements as a result of adoption of the new standard is immaterial. Based on the nature of the contracts with our customers and our related performance obligations which transfer control, a $0.5 million after-tax cumulative‑effect transition adjustment was made to increase the opening balance of Retained Earnings. We have included additional disclosures in the notes to the consolidated financial statements including additional information on the Company’s revenue streams and related performance obligations required to be satisfied in order to recognize revenue. (See Revenue Recognition.) Practical Expedients The following practical expedients were used by the Company as part of the adoption of the new revenue recognition guidance:
Recently Issued Pronouncements Simplifying the Test for Goodwill Impairment. In January 2017, the FASB issued updated guidance which simplifies the measurement of goodwill impairment by removing step two of the goodwill impairment test that requires the determination of the fair value of individual assets and liabilities of a reporting unit. The updated guidance requires goodwill impairment to be measured as the amount by which a reporting unit’s carrying value exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. This guidance is effective for the Company beginning in the first quarter of 2020, with early adoption permitted on a prospective basis. Leases. In 2016, the FASB issued an accounting standard update which revises the existing guidance for leases. Under the revised guidance, lessees will be required to recognize a “right-of-use” asset and a lease liability for all leases with a term greater than 12 months. The new standard also requires additional quantitative and qualitative disclosures by lessees and lessors to enable users of the financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. The accounting for leases by lessors and the recognition, measurement, and presentation of expenses and cash flows from leases are not expected to significantly change as a result of the new guidance. We expect to make approximately $80 million in minimum lease payments due in future years (undiscounted). The revised guidance is effective for the Company beginning in the first quarter of 2019 with early adoption permitted. We are currently evaluating the impact of the revised lease guidance on our Consolidated Financial Statements. NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) Income Taxes. Under SEC Staff Accounting Bulletin 118 (SAB 118), which was issued in December 2017, companies are allowed up to one year to complete the required analyses and accounting for the TCJA. SAB 118 requires companies to disclose which tax positions are considered complete, which tax positions are considered provisional and which tax provisions reflect prior law. At December 31, 2017, we were reasonably able to estimate the effects of the TCJA, and therefore recorded provisional amounts associated with the changes under the TCJA. The provisional amounts incorporate assumptions made based upon the Company’s interpretation of the TCJA, and may change as the Company receives additional clarification and implementation guidance. We have not made any adjustments to our accounting to date, although the accounting is still considered provisional while we complete our analysis. Any adjustments recorded to the provisional amounts in 2018 will be included in income from operations as an adjustment to income tax expense. |
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- Definition The entire disclosure for the general note to the financial statements for the reporting entity which may include, descriptions of the basis of presentation, business description, significant accounting policies, consolidations, reclassifications, new pronouncements not yet adopted and changes in accounting principles. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Investments |
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| Investments [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Investments [Text Block] | INVESTMENTS Investments. As of June 30, 2018, the investment portfolio included the legacy real estate assets of ALLETE Properties, debt and equity securities consisting primarily of securities held in other postretirement plans to fund employee benefits, the cash equivalents within these plans and other assets consisting primarily of land in Minnesota.
Available-for-Sale Securities. We account for our available-for-sale securities portfolio in accordance with the guidance for certain investments in debt and equity securities. Our available-for-sale securities portfolio consisted primarily of securities held in other postretirement plans to fund employee benefits. Gross realized and unrealized gains and losses on our available-for-sale securities were immaterial for the quarter and six months ended June 30, 2018, and 2017. |
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- Definition The entire disclosure for investments, including all tables. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Acquisitions |
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| Business Combinations [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Acquisitions [Text Block] | ACQUISITIONS The following acquisition is consistent with ALLETE’s stated strategy of investing in energy infrastructure and related services businesses to complement its regulated businesses, balance exposure to business cycles and changing demand, and provide potential long-term earnings growth. The pro forma impact of the following acquisitions was not significant, either individually or in the aggregate, to the results of the Company for the six months ended June 30, 2018, and 2017. 2017 Activity. Tonka Water. In September 2017, U.S. Water Services acquired 100 percent of Tonka Water. Total consideration for the transaction was $19.2 million, including a working capital adjustment. Consideration of $19.0 million was paid in cash on the acquisition date and a working capital adjustment of $0.2 million was paid in the fourth quarter of 2017. Tonka Water is a supplier of municipal and industrial water treatment systems and will expand U.S. Water Services’ geographic and customer markets. NOTE 3. ACQUISITIONS (Continued) 2017 Activity (Continued) The acquisition was accounted for as a business combination and the purchase price was allocated based on the estimated fair values of the assets acquired and the liabilities assumed at the date of acquisition. The purchase price accounting, which was finalized in 2018, is reflected in the following table. Fair value measurements were valued primarily using the discounted cash flow method and replacement cost basis.
Acquisition-related costs were immaterial, expensed as incurred during 2017 and recorded in Operating and Maintenance on the Consolidated Statement of Income. |
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- Definition The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Goodwill and Intangible Assets |
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| Goodwill and Intangible Assets Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Goodwill and Intangible Assets [Text Block] | GOODWILL AND INTANGIBLE ASSETS The aggregate carrying amount of goodwill was $148.5 million as of June 30, 2018, and $148.3 million as of December 31, 2017. Balances of intangible assets, net, excluding goodwill as of June 30, 2018, are as follows:
Customer relationships have a remaining useful life of approximately 20 years, and developed technology and other have remaining useful lives ranging from approximately 1 year to approximately 11 years (weighted average of approximately 6 years). The weighted average remaining useful life of all definite-lived intangible assets as of June 30, 2018, is approximately 18 years. NOTE 4. GOODWILL AND INTANGIBLE ASSETS (Continued) Amortization expense for intangible assets was $1.3 million and $2.7 million for the quarter and six months ended June 30, 2018, respectively ($1.4 million and $2.8 million for the quarter and six months ended June 30, 2017, respectively). Accumulated amortization was $17.5 million as of June 30, 2018 ($14.8 million as of December 31, 2017). The estimated amortization expense for definite-lived intangible assets for the remainder of 2018 is $2.8 million. Estimated annual amortization expense for definite‑lived intangible assets is $5.2 million in 2019, $5.0 million in 2020, $4.9 million in 2021, $4.6 million in 2022 and $38.2 million thereafter. |
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- Definition The entire disclosure for goodwill and intangible assets. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Fair Value |
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| Fair Value Disclosures [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fair Value [Text Block] | FAIR VALUE Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We utilize market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated or generally unobservable. We primarily apply the market approach for recurring fair value measurements and endeavor to utilize the best available information. Accordingly, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs, which are used to measure fair value, are prioritized through the fair value hierarchy. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). Descriptions of the three levels of the fair value hierarchy are discussed in Note 9. Fair Value to the Consolidated Financial Statements in our 2017 Form 10-K. The following tables set forth by level within the fair value hierarchy our assets and liabilities that were accounted for at fair value on a recurring basis as of June 30, 2018, and December 31, 2017. Each asset and liability is classified based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement requires judgment, which may affect the valuation of these assets and liabilities and their placement within the fair value hierarchy levels. The estimated fair value of Cash and Cash Equivalents listed on the Consolidated Balance Sheet approximates the carrying amount and therefore is excluded from the recurring fair value measures in the following tables.
NOTE 5. FAIR VALUE (Continued)
The Level 3 liability in the preceding tables is the result of the 2015 acquisition of U.S. Water Services. Changes in the U.S. Water Services Contingent Consideration can result from modifications to the shareholder agreement, changes in discount rates, timing of milestones that trigger payment, or the timing and amount of earnings estimates. The following table provides a reconciliation of the beginning and ending balances of the U.S. Water Services Contingent Consideration measured at fair value using Level 3 measurements as of June 30, 2018. Management analyzes the fair value of the contingent liability on a quarterly basis and makes adjustments as appropriate.
For the six months ended June 30, 2018, and the year ended December 31, 2017, there were no transfers in or out of Levels 1, 2 or 3. Fair Value of Financial Instruments. With the exception of the item listed in the following table, the estimated fair value of all financial instruments approximates the carrying amount. The fair value for the item listed in the following table was based on quoted market prices for the same or similar instruments (Level 2).
Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis. Non-financial assets such as equity method investments, goodwill, intangible assets, land inventory, and property, plant and equipment are measured at fair value when there is an indicator of impairment and recorded at fair value only when an impairment is recognized. For the quarter and six months ended June 30, 2018, and the year ended December 31, 2017, there were no triggering events or indicators of impairment for these non-financial assets. |
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- Definition The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Regulatory Matters |
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| Regulatory Matters [Text Block] | REGULATORY MATTERS Regulatory matters are summarized in Note 4. Regulatory Matters to our Consolidated Financial Statements in our 2017 Form 10‑K, with additional disclosure provided in the following paragraphs. Electric Rates. Entities within our Regulated Operations segment file for periodic rate revisions with the MPUC, PSCW or FERC. As authorized by the MPUC, Minnesota Power also recognizes revenue under cost recovery riders for transmission, renewable, and environmental investments and expenditures. (See Transmission Cost Recovery Rider, Renewable Cost Recovery Rider and Environmental Improvement Rider.) Revenue from cost recovery riders was $28.0 million and $52.1 million for the quarter and six months ended June 30, 2018, respectively ($24.4 million and $48.6 million for the quarter and six months ended June 30, 2017, respectively). 2016 Minnesota General Rate Case. In November 2016, Minnesota Power filed a retail rate increase request with the MPUC which sought an average increase of approximately 9 percent for retail customers. The rate filing sought a return on equity of 10.25 percent and a 53.81 percent equity ratio. On an annualized basis, the requested final rate increase would have generated approximately $55 million in additional revenue. In December 2016, Minnesota Power filed a request to modify its original interim rate proposal, reducing its requested interim rate increase to $34.7 million from the original request of approximately $49 million due to a change in its electric sales forecast. In December 2016 orders, the MPUC accepted the November 2016 filing as complete and authorized an annual interim rate increase of $34.7 million beginning in January 2017. In February 2017, Minnesota Power filed an additional request to further reduce its requested interim rate increase. In an April 2017 order, the MPUC approved Minnesota Power’s updated retail rate request resulting in a reduction in the annual interim rate increase to $32.2 million beginning in May 2017. As a result of working with intervenors and further developments as the rate review progressed, Minnesota Power’s final rate request was adjusted to approximately $49 million on an annualized basis. In an order dated March 12, 2018, the MPUC affirmed determinations made at a hearing on January 18, 2018, regarding Minnesota Power’s general rate case including allowing a return on common equity of 9.25 percent and a 53.81 percent equity ratio. Upon commencement of final rates, we expect additional revenue of approximately $13 million on an annualized basis. Final rates are expected to commence in the fourth quarter of 2018; interim rates will be collected through this period which are fully offset by the recognition of a corresponding reserve. Minnesota Power has recorded a reserve for an interim rate refund of $49.2 million as of June 30, 2018 ($32.3 million as of December 31, 2017). The MPUC also disallowed Minnesota Power’s regulatory asset for deferred fuel adjustment clause costs due to the anticipated adoption of a forward-looking fuel adjustment clause methodology resulting in a $19.5 million pre-tax charge to Fuel, Purchased Power and Gas – Utility in the fourth quarter of 2017. As part of its decision in Minnesota Power’s 2016 general rate case, the MPUC extended the depreciable lives of Boswell Unit 3, Unit 4 and common facilities to 2050 primarily to mitigate rate increases for our customers, and shortened the depreciable lives of Boswell Unit 1 and Unit 2 to 2022, resulting in a net decrease to depreciation expense of approximately $25 million in the fourth quarter of 2017. On April 2, 2018, Minnesota Power filed a petition with the MPUC requesting reconsideration of certain decisions in the MPUC’s order dated March 12, 2018, collectively representing approximately $20 million to $25 million in additional revenue on an annualized basis. Minnesota Power’s petition included requesting reconsideration of the allowed return on common equity, recovery of the prepaid pension asset in rate base, certain disallowed expenses, and certain transmission revenue adjustments. In an order dated May 29, 2018, the MPUC denied Minnesota Power’s petition for reconsideration and accepted a Minnesota Department of Commerce request for reconsideration reducing the depreciable lives of Boswell Unit 3, Unit 4 and common facilities to 2035 while utilizing the benefits of the lower federal income tax rate enacted as part of the TCJA to mitigate the impact on customer rates. Energy-Intensive Trade-Exposed Customer Rates. An EITE customer ratemaking law was enacted in 2015, which established a Minnesota energy policy to have competitive rates for certain industries such as mining and forest products. In 2015, Minnesota Power filed a rate schedule petition with the MPUC for EITE customers and a corresponding rider for EITE cost recovery. In a March 2016 order, the MPUC dismissed the petition without prejudice. In June 2016, Minnesota Power filed a revised EITE petition with the MPUC which included additional information on the net benefits analysis, limits on eligible customers and term lengths for the EITE discount. The rate adjustments were intended to be revenue and cash flow neutral to Minnesota Power. The MPUC approved a reduction in rates for EITE customers in a December 2016 order and subsequently approved cost recovery in an April 2017 order; collection of the discount was subject to the MPUC’s review of Minnesota Power’s compliance filing implementing approval of a recovery mechanism, with the subsequent order issued in October 2017 that modified the April 2017 order. During 2017, Minnesota Power provided discounts of $8.6 million that were recorded as a regulatory asset. NOTE 6. REGULATORY MATTERS (Continued) Electric Rates (Continued) In September 2017, Minnesota Power informed its EITE customers that it had suspended the EITE discount due to a concern that it was not revenue and cash flow neutral to Minnesota Power based on an MPUC decision at a hearing in September 2017, as well as the interim rate reduction and decisions in its 2016 general rate case. Based on the MPUC’s decisions at a hearing on January 18, 2018, as part of Minnesota Power’s 2016 general rate case, Minnesota Power reinstated the EITE discount effective January 1, 2018. Minnesota Power expects the discount to EITE customers to be approximately $15 million annually based on EITE customer current operating levels. While interim rates are in effect for Minnesota Power’s 2016 general rate case, discounts provided to EITE customers will offset interim rate refund reserves for non-EITE customers. Minnesota Power provided $3.8 million and $8.1 million of discounts to EITE customers during the quarter and six months ended June 30, 2018, respectively ($3.6 million and $5.9 million for the quarter and six months ended June 30, 2017, respectively). FERC-Approved Wholesale Rates. Minnesota Power has 16 non-affiliated municipal customers in Minnesota. SWL&P is a Wisconsin utility and a wholesale customer of Minnesota Power. All wholesale contracts include a termination clause requiring a three-year notice to terminate. Minnesota Power’s wholesale electric contract with the Nashwauk Public Utilities Commission is effective through at least December 31, 2032. No termination notice may be given for this contract prior to July 1, 2029. The wholesale electric service contracts with SWL&P and another municipal customer are effective through at least August 31, 2021, and through June 30, 2019, respectively. Under the agreement with SWL&P, no termination notice has been given. The other municipal customer provided termination notice for its contract in 2016. Minnesota Power currently provides approximately 29 MW of average monthly demand to this customer. The rates included in these three contracts are set each July 1 based on a cost-based formula methodology, using estimated costs and a rate of return that is equal to Minnesota Power’s authorized rate of return for Minnesota retail customers. The formula-based rate methodology also provides for a yearly true-up calculation for actual costs incurred. Minnesota Power’s wholesale electric contracts with 14 municipal customers are effective through varying dates ranging from 2024 through 2029 with a majority effective through at least December 31, 2024. No termination notices may be given prior to three years before maturity. These contracts include fixed capacity charges through 2018; beginning in 2019, the capacity charge will be determined using a cost-based formula methodology with limits on the annual change from the previous year’s capacity charge. The base energy charge for each year of the contract term will be set each January 1, subject to monthly adjustment, and will also be determined using a cost-based formula methodology. Transmission Cost Recovery Rider. Minnesota Power has an approved cost recovery rider for certain transmission investments and expenditures. In a 2016 order, the MPUC approved Minnesota Power’s updated customer billing rates allowing Minnesota Power to charge retail customers on a current basis for the costs of constructing certain transmission facilities plus a return on the capital invested. As a result of the MPUC approval of the certificate of need for the GNTL in 2015, the project is eligible for cost recovery under the existing transmission cost recovery rider. Minnesota Power is funding the construction of the GNTL with a subsidiary of Manitoba Hydro (see Great Northern Transmission Line), and anticipates including its portion of the investments and expenditures for the GNTL in future transmission bill factor filings. Renewable Cost Recovery Rider. Minnesota Power has an approved cost recovery rider for investments and expenditures related to Bison. The cost recovery rider allows Minnesota Power to charge retail customers on a current basis for the costs of certain renewable investments plus a return on the capital invested. Updated customer billing rates for the renewable cost recovery rider were approved by the MPUC in a November 2017 order. On June 5, 2018, Minnesota Power made a renewable resources factor filing. Upon approval of the filing, Minnesota Power will be authorized to include updated billing rates on customer bills. Minnesota Power also has approval for current cost recovery of investments and expenditures related to compliance with the Minnesota Solar Energy Standard. (See Minnesota Solar Energy Standard.) Currently, there is no approved customer billing rate for solar costs. Environmental Improvement Rider. Minnesota Power has an approved environmental improvement rider for investments and expenditures related to the implementation of the Boswell Unit 4 mercury emissions reduction plan completed in 2015. Updated customer billing rates for the environmental improvement rider were provisionally approved by the MPUC in an order dated June 20, 2018, subject to further review by the MPUC. NOTE 6. REGULATORY MATTERS (Continued) Electric Rates (Continued) Fuel Adjustment Clause Reform. In a December 2017 order, the MPUC adopted a three-year program to implement certain procedural reforms to the Minnesota utilities’ automatic fuel adjustment clause (FAC) for fuel and purchased power. The order will change the method of accounting for all Minnesota electric utilities to a monthly budgeted, forward-looking FAC with an annual prudence review and true-up to actual allowed costs. The MPUC is seeking input from Minnesota electric utilities and other stakeholders on the implementation and transition accounting needed to adopt the change. The three-year program is expected to begin in 2019. Tax Cuts and Jobs Act of 2017. In December 2017, the MPUC opened a docket to review the effects of the TCJA on electric and natural gas rates and services in Minnesota, including the legislation’s impact on tax rates and utilities’ deferred income tax assets and liabilities. On March 2, 2018, Minnesota Power submitted an initial filing to the MPUC regarding the impacts of the TCJA on Minnesota Power. As part of Minnesota Power’s rate case, in an order dated May 29, 2018, the MPUC directed Minnesota Power to utilize the benefits of lower federal income tax rates enacted as part of the TCJA to offset a reduction in the depreciable lives of Boswell Unit 3, Unit 4 and common facilities to 2035 that would have otherwise resulted in an increase in customer rates. The treatment of the impact of the TCJA on Minnesota Power’s deferred income tax assets and liabilities is still subject to this regulatory proceeding. On January 10, 2018, the PSCW opened a docket to review the effects of the TCJA and directed Wisconsin utilities to defer its impacts until further direction was provided by the PSCW. On February 9, 2018, SWL&P filed comments with the PSCW regarding the impacts of the TCJA on SWL&P. In this filing, SWL&P proposed deferring the benefits of the TCJA and incorporating any deferred refunds or credits into its next general rate case. In an order dated May 24, 2018, the PSCW directed SWL&P to refund the benefits of the lower federal income tax rates enacted as part of the TCJA on customer bills beginning in July 2018. Any changes in deferred income taxes will be adjusted as part of SWL&P’s rate filing. (See 2018 Wisconsin General Rate Case.) We have recorded the impact of the remeasurement of deferred income tax assets and liabilities in 2017 resulting from the TCJA for Minnesota Power and SWL&P as regulatory assets and liabilities as the benefits are deferred pending the outcome of regulatory proceedings. Most of the benefits for Minnesota Power and SWL&P are expected to be passed back to customers over time primarily based upon the normalization provisions of the U.S. Internal Revenue Code over the life of the related property, plant and equipment with the remainder expected to be passed back based upon the outcome of regulatory proceedings. We are unable to predict the outcome of these regulatory proceedings. 2016 Wisconsin General Rate Case. SWL&P’s current retail rates are based on a 2017 PSCW retail rate order effective since August 2017 that allows for a 10.5 percent return on common equity and a 55 percent equity ratio. SWL&P’s retail rates prior to August 2017 were based on a 2012 PSCW retail rate order that provided for a 10.9 percent return on equity. On an annualized basis, SWL&P expects to collect additional revenue of $2.5 million under the 2017 PSCW retail rate order. 2018 Wisconsin General Rate Case. On May 25, 2018, SWL&P filed a rate increase request with the PSCW requesting an average increase of 2.7 percent for retail customers (2.0 percent increase in electric rates; 2.3 percent increase in natural gas rates; and 8.3 percent increase in water rates). The filing seeks an overall return on equity of 10.5 percent and a 55.41 percent equity ratio. On an annualized basis, this filing is expected to result in additional revenue of approximately $2.4 million. Integrated Resource Plan. In 2015, Minnesota Power filed its 2015 IRP with the MPUC, which included an analysis of a variety of existing and future energy resource alternatives and a projection of customer cost impact by class. The 2015 IRP also contained steps in Minnesota Power’s EnergyForward strategic plan including the economic idling of Taconite Harbor Units 1 and 2 which occurred in 2016, the ceasing of coal-fired operations at Taconite Harbor in 2020, and the addition of between 200 MW and 300 MW of natural gas-fired generation in the next decade. In a 2016 order, the MPUC approved Minnesota Power’s 2015 IRP with modifications. The order accepted Minnesota Power’s plans for Taconite Harbor, directed Minnesota Power to retire Boswell Units 1 and 2 no later than 2022, required an analysis of generation and demand response alternatives to be filed with a natural gas resource proposal, and required Minnesota Power to conduct request for proposals for additional wind, solar and demand response resource additions subject to further MPUC approvals. In 2016, Minnesota Power announced Boswell Units 1 and 2 will be retired, which is expected to occur in the fourth quarter of 2018. NOTE 6. REGULATORY MATTERS (Continued) Integrated Resource Plan (Continued) In July 2017, Minnesota Power submitted a resource package to the MPUC requesting approval of PPAs for the output of a 250 MW wind energy facility and a 10 MW solar energy facility as well as approval of a 250 MW natural gas energy PPA. These agreements are subject to MPUC approval of the construction of NTEC, a 525 MW to 550 MW combined‑cycle natural gas‑fired generating facility which will be jointly owned by Dairyland Power Cooperative and a subsidiary of ALLETE. Minnesota Power would purchase approximately 50 percent of the facility's output starting in 2025. In a September 2017 order, the MPUC approved Minnesota Power’s request to extend the next IRP filing deadline until October 1, 2019, and Minnesota Power’s request that approval for the natural gas energy PPA be decided through a contested case process. On July 2, 2018, an administrative law judge issued a recommendation that the MPUC deny approval of the NTEC agreements; the recommendation is not binding on the MPUC. On July 23, 2018, Minnesota Power filed exceptions to the administrative law judge’s recommendation. The MPUC is expected to hold a hearing in the fourth quarter of 2018 on NTEC. On June 18, 2018, Minnesota Power filed a separate petition for approval of the PPA for the output of a 10 MW solar energy facility located in central Minnesota. The MPUC has not taken any action regarding the wind energy PPA which will be refiled separately from the natural gas energy PPA. Great Northern Transmission Line. Minnesota Power is constructing the GNTL, an approximately 220-mile 500-kV transmission line between Manitoba and Minnesota’s Iron Range that was proposed by Minnesota Power and Manitoba Hydro. In 2015, a certificate of need was approved by the MPUC. Based on this approval, Minnesota Power’s portion of the investments and expenditures for the project are eligible for cost recovery under its existing transmission cost recovery rider and are anticipated to be included in future transmission cost recovery filings. (See Transmission Cost Recovery Rider.) Also in 2015, the FERC approved our request to recover on construction work in progress related to the GNTL from Minnesota Power’s wholesale customers. In a 2016 order, the MPUC approved the route permit for the GNTL which largely follows Minnesota Power’s preferred route, including the international border crossing, and in 2016, the U.S. Department of Energy issued a presidential permit to cross the U.S.-Canadian border, which was the final major regulatory approval needed before construction in the U.S. could begin. Site clearing and pre‑construction activities commenced in the first quarter of 2017 with construction expected to be completed in 2020. To date, most of the right-of-way has been cleared while foundation installation and transmission tower construction have commenced. The total project cost in the U.S., including substation work, is estimated to be between $560 million and $710 million, of which Minnesota Power’s portion is expected to be between $300 million and $350 million; the difference will be recovered from a subsidiary of Manitoba Hydro as non-shareholder contributions to capital. Total project costs of $248.8 million have been incurred through June 30, 2018, of which $129.2 million has been recovered from a subsidiary of Manitoba Hydro. Manitoba Hydro must obtain regulatory and governmental approvals related to a new transmission line in Canada known as the Manitoba-Minnesota Transmission Project (MMTP) that will connect with the GNTL. In 2015, Manitoba Hydro submitted the final preferred route and EIS for the MMTP to the Manitoba Conservation and Water Stewardship for siting and environmental approval, which remains pending. In 2016, Manitoba Hydro filed an application with the Canadian National Energy Board (NEB) requesting authorization to construct and operate the MMTP. The NEB determined that Manitoba Hydro’s application was complete in December 2017, and held public hearings in June 2018. The NEB is required to make a decision on the MMTP by March 2019, but is not precluded from making a decision prior to that date. Approval of the Canadian federal cabinet is also required. The MMTP is subject to legal and regulatory challenges which Minnesota Power is actively monitoring. Manitoba Hydro has informed Minnesota Power that it continues to work towards completing the MMTP on schedule. In order to meet the transmission in‑service requirements in PPAs with Minnesota Power, Manitoba Hydro has indicated that it would need to start construction of the MMTP in December 2018. We are unable to predict the outcome of the Canadian regulatory review process, including the timing thereof or whether any onerous conditions may be imposed, or the timing of the completion of the MMTP, including the impact of any delays that may result in construction schedule adjustments. Any significant delays in the MMTP construction schedule may result in Minnesota Power adjusting the GNTL construction schedule and impact the timing of capital expenditures and associated cost recovery under our transmission cost recovery rider. Construction of Manitoba Hydro’s Keeyask hydroelectric generation facility, which will provide the power to be sold under PPAs with Minnesota Power and transmitted on the MMTP and the GNTL, commenced in 2014 and is anticipated to be in service by early 2021. NOTE 6. REGULATORY MATTERS (Continued) Conservation Improvement Program. Minnesota requires electric utilities to spend a minimum of 1.5 percent of gross operating revenues, excluding revenue received from exempt customers, from service provided in the state on energy CIPs each year. On April 2, 2018, Minnesota Power submitted its 2017 CIP consolidated filing, which detailed Minnesota Power’s CIP program results and requested a CIP financial incentive of $3.3 million based upon MPUC procedures. In 2017, the CIP financial incentive of $5.5 million was recognized in the second quarter upon approval by the MPUC of Minnesota Power’s 2016 CIP consolidated filing in a June 2017 order. Approval of Minnesota Power’s 2017 CIP consolidated filing and related financial incentive is expected in the third quarter of 2018. CIP financial incentives are recognized in the period in which the MPUC approves the filing. MISO Return on Equity Complaints. MISO transmission owners, including ALLETE and ATC, have an authorized return on equity of 10.32 percent, or 10.82 percent including an incentive adder for participation in a regional transmission organization. In 2016, a federal administrative law judge ruled on a complaint proposing a reduction in the base return on equity to 9.70 percent, or 10.20 percent including an incentive adder for participation in a regional transmission organization, subject to approval or adjustment by the FERC. A final decision from the FERC on the administrative law judge’s recommendation is pending, which is not expected to have a material impact on our Consolidated Financial Statements. Minnesota Solar Energy Standard. Minnesota law requires at least 1.5 percent of total retail electric sales, excluding sales to certain customers, to be generated by solar energy by the end of 2020. At least 10 percent of the 1.5 percent mandate must be met by solar energy generated by or procured from solar photovoltaic devices with a nameplate capacity of 40 kW or less and community solar garden subscriptions. In a 2016 order, the MPUC approved Camp Ripley, a 10 MW utility scale solar project at the Camp Ripley Minnesota Army National Guard base and training facility near Little Falls, Minnesota, as eligible to meet the solar energy standard and for current cost recovery. Camp Ripley was completed in the fourth quarter of 2016. In a 2016 order, the MPUC approved a community solar garden project in northeastern Minnesota, which is comprised of a 1 MW solar array owned and operated by a third party with the output purchased by Minnesota Power and a 40 kW solar array that is owned and operated by Minnesota Power. Minnesota Power believes Camp Ripley and the community solar garden arrays will meet approximately one‑third of the overall mandate. Additionally, in a February 2017 order, the MPUC approved Minnesota Power’s proposal to increase the amount of solar rebates available for customer-sited solar installations and recover costs of the program through Minnesota Power’s renewable cost recovery rider. The proposal to incentivize customer‑sited solar installations and community solar garden subscriptions is expected to meet a portion of the required small scale solar mandate. Regulatory Assets and Liabilities. Our regulated utility operations are subject to accounting guidance for the effect of certain types of regulation. Regulatory assets represent incurred costs that have been deferred as they are probable for recovery in customer rates. Regulatory liabilities represent obligations to make refunds to customers and amounts collected in rates for which the related costs have not yet been incurred. The Company assesses quarterly whether regulatory assets and liabilities meet the criteria for probability of future recovery or deferral. No regulatory assets or liabilities are currently earning a return. The recovery, refund or credit to rates for these regulatory assets and liabilities will occur over the periods either specified by the applicable regulatory authority or over the corresponding period related to the asset or liability. NOTE 6. REGULATORY MATTERS (Continued)
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- Definition The entire disclosure for public utilities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Investment in ATC |
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| Investment in ATC [Text Block] | INVESTMENT IN ATC Our wholly-owned subsidiary, ALLETE Transmission Holdings, owns approximately 8 percent of ATC, a Wisconsin-based utility that owns and maintains electric transmission assets in portions of Wisconsin, Michigan, Minnesota and Illinois. We account for our investment in ATC under the equity method of accounting. As of June 30, 2018, our equity investment in ATC was $123.6 million ($118.7 million at December 31, 2017). In the first six months of 2018, we invested $3.9 million in ATC, and on July 31, 2018, we invested an additional $1.2 million. We expect to make additional investments of $1.3 million in 2018.
(a) Amortization related to the impact of the remeasurement of deferred income tax assets and liabilities resulting from the TCJA. NOTE 7. INVESTMENT IN ATC (Continued) ATC’s authorized return on equity is 10.32 percent, or 10.82 percent including an incentive adder for participation in a regional transmission organization. In 2016, a federal administrative law judge ruled on a complaint proposing a reduction in the base return on equity to 9.70 percent, or 10.20 percent including an incentive adder for participation in a regional transmission organization, subject to approval or adjustment by the FERC. A final decision from the FERC on the administrative law judge’s recommendation is pending. |
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- Definition The entire disclosure for equity method investments and joint ventures. Equity method investments are investments that give the investor the ability to exercise significant influence over the operating and financial policies of an investee. Joint ventures are entities owned and operated by a small group of businesses as a separate and specific business or project for the mutual benefit of the members of the group. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| Short-Term and Long-Term Debt [Text Block] | SHORT-TERM AND LONG-TERM DEBT The following tables present the Company’s short-term and long-term debt as of June 30, 2018, and December 31, 2017:
On April 16, 2018, ALLETE issued and sold $60.0 million of its First Mortgage Bonds (the Bonds) that bear interest at 4.07 percent. The Bonds will mature in April 2048 and pay interest semi-annually in April and October of each year, commencing on October 16, 2018. ALLETE has the option to prepay all or a portion of the Bonds at its discretion, subject to a make-whole provision. The Bonds are subject to additional terms and conditions which are customary for these types of transactions. ALLETE intends to use the proceeds from the sale of the Bonds to fund utility capital investment and for general corporate purposes. The Bonds were sold in reliance on an exemption from registration under Section 4(a)(2) of the Securities Act of 1933, as amended, to institutional accredited investors. Financial Covenants. Our long-term debt arrangements contain customary covenants. In addition, our lines of credit and letters of credit supporting certain long-term debt arrangements contain financial covenants. Our compliance with financial covenants is not dependent on debt ratings. The most restrictive financial covenant requires ALLETE to maintain a ratio of indebtedness to total capitalization (as the amounts are calculated in accordance with the respective long-term debt arrangements) of less than or equal to 0.65 to 1.00, measured quarterly. As of June 30, 2018, our ratio was approximately 0.42 to 1.00. Failure to meet this covenant would give rise to an event of default if not cured after notice from the lender, in which event ALLETE may need to pursue alternative sources of funding. Some of ALLETE’s debt arrangements contain “cross-default” provisions that would result in an event of default if there is a failure under other financing arrangements to meet payment terms or to observe other covenants that would result in an acceleration of payments due. ALLETE has no significant restrictions on its ability to pay dividends from retained earnings or net income. As of June 30, 2018, ALLETE was in compliance with its financial covenants. |
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- Definition The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| Income Tax Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Income Tax Expense [Text Block] | INCOME TAX EXPENSE
The Company's tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items arising in that quarter. In each quarter, the Company updates its estimate of the annual effective tax rate, and if the estimated annual effective tax rate changes, the Company would make a cumulative adjustment in that quarter.
For the six months ended June 30, 2018, the effective tax rate was a benefit of 12.4 percent (expense of 19.2 percent for the six months ended June 30, 2017). Uncertain Tax Positions. As of June 30, 2018, we had gross unrecognized tax benefits of $1.7 million ($1.7 million as of December 31, 2017). Of the total gross unrecognized tax benefits, $0.8 million represents the amount of unrecognized tax benefits included on the Consolidated Balance Sheet that, if recognized, would favorably impact the effective income tax rate. The unrecognized tax benefit amounts have been presented as reductions to the tax benefits associated with NOL and tax credit carryforwards on the Consolidated Balance Sheet. ALLETE and its subsidiaries file a consolidated federal income tax return as well as combined and separate state income tax returns in various jurisdictions. ALLETE has no open federal or state audits, and is no longer subject to federal examination for years before 2014, or state examination for years before 2013. |
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- Definition The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reclassifications Out of Accumulated Other Comprehensive Loss |
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| Equity [Abstract] | |
| Reclassifications Out of Accumulated Other Comprehensive Income (Loss) [Text Block] | RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE LOSS Changes in Accumulated Other Comprehensive Loss. Comprehensive income (loss) is the change in shareholders’ equity during a period from transactions and events from non-owner sources, including net income. The amounts recorded to accumulated other comprehensive loss include unrealized gains and losses on available-for-sale debt securities and defined benefit pension and other postretirement items, consisting of deferred actuarial gains or losses and prior service costs or credits. For the quarter and six months ended June 30, 2018, and 2017, reclassifications out of accumulated other comprehensive loss for the Company were not material. Changes in accumulated other comprehensive loss for the six months ended June 30, 2018, are presented on the Consolidated Statement of Shareholders’ Equity. |
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- Definition The entire disclosure for any adjustments made during the period to avoid double counting in comprehensive income items displayed as part of net income that also had been displayed as part of other comprehensive income in that period or earlier periods. These adjustments include reclassifications to net income of items in accumulated comprehensive income, such as deferred gains or losses on qualifying hedges when hedged item reported in net income, holding gains or losses on available-for-sale securities transferred into trading category, unrealized holding gains or losses on debt securities transferred from held-to-maturity category into available-for-sale category and accumulated translation adjustment attributable to foreign subsidiary or investment in foreign entity upon sale or liquidation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Earnings Per Share and Common Stock |
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| Earnings Per Share [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Earnings Per Share and Common Stock [Text Block] | EARNINGS PER SHARE AND COMMON STOCK We compute basic earnings per share using the weighted average number of shares of common stock outstanding during each period. The difference between basic and diluted earnings per share, if any, arises from outstanding stock options, non-vested restricted stock units and performance share awards granted under our Executive Long-Term Incentive Compensation Plan. For the quarter and six months ended June 30, 2018, and 2017, no options to purchase shares of ALLETE common stock were excluded from the computation of diluted earnings per share.
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- Definition The entire disclosure for earnings per share. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Pension and Other Postretirement Benefit Plans |
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| Retirement Benefits [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Pension and Other Postretirement Benefit Plans [Text Block] | PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS
NOTE 12. PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Continued) Employer Contributions. For the six months ended June 30, 2018, we contributed $15.0 million in cash to the defined benefit pension plans ($1.7 million in cash and $13.5 million in ALLETE common stock for the six months ended June 30, 2017); we do not expect to make additional contributions to our defined benefit pension plans in 2018. For the six months ended June 30, 2018, and 2017, we made no contributions to our other postretirement benefit plans; we do not expect to make any contributions to our other postretirement benefit plans in 2018. |
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- Definition The entire disclosure for pension and other postretirement benefits. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Commitments, Guarantees and Contingencies |
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| Commitments and Contingencies Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||
| Commitments, Guarantees and Contingencies [Text Block] | COMMITMENTS, GUARANTEES AND CONTINGENCIES Power Purchase Agreements. Our long-term PPAs have been evaluated under the accounting guidance for variable interest entities. We have determined that either we have no variable interest in the PPAs or, where we do have variable interests, we are not the primary beneficiary; therefore, consolidation is not required. These conclusions are based on the fact that we do not have both control over activities that are most significant to the entity and an obligation to absorb losses or receive benefits from the entity’s performance. Our financial exposure relating to these PPAs is limited to our capacity and energy payments. Our PPAs are summarized in Note 11. Commitments, Guarantees and Contingencies to our Consolidated Financial Statements in our 2017 Form 10-K, with additional disclosure provided in the following paragraphs. Square Butte PPA. Minnesota Power has a PPA with Square Butte that extends through 2026 (Agreement). Minnesota Power is obligated to pay its pro rata share of Square Butte’s costs based on its entitlement to the output of Square Butte’s 455 MW coal‑fired generating unit. Minnesota Power’s output entitlement under the Agreement is 50 percent for the remainder of the Agreement, subject to the provisions of the Minnkota Power PSA. (See Minnkota Power PSA.) Square Butte’s costs consist primarily of debt service, operating and maintenance, depreciation and fuel expenses. As of June 30, 2018, Square Butte had total debt outstanding of $311.4 million. Fuel expenses are recoverable through Minnesota Power’s fuel adjustment clause and include the cost of coal purchased from BNI Energy under a long-term contract. Minnesota Power’s cost of power purchased from Square Butte during the six months ended June 30, 2018, was $37.7 million ($40.7 million for the six months ended June 30, 2017). This reflects Minnesota Power’s pro rata share of total Square Butte costs based on the 50 percent output entitlement. Included in this amount was Minnesota Power’s pro rata share of interest expense of $4.6 million ($4.7 million for the same period in 2017). Minnesota Power’s payments to Square Butte are approved as a purchased power expense for ratemaking purposes by both the MPUC and the FERC. Minnkota Power PSA. Minnesota Power has a PSA with Minnkota Power, which commenced in 2014. Under the PSA, Minnesota Power is selling a portion of its entitlement from Square Butte to Minnkota Power, resulting in Minnkota Power’s net entitlement increasing and Minnesota Power’s net entitlement decreasing until Minnesota Power’s share is eliminated at the end of 2025. Of Minnesota Power’s 50 percent output entitlement, it sold to Minnkota Power approximately 28 percent in 2018 and in 2017. Oconto Electric Cooperative PSA. On March 6, 2018, Minnesota Power entered into a PSA with Oconto Electric Cooperative. The contract begins in January 2019 and is effective through May 2026. Under the PSA, Minnesota Power expects to provide approximately 25 MW of energy and capacity at fixed prices. Coal, Rail and Shipping Contracts. Minnesota Power has coal supply agreements providing for the purchase of a significant portion of its coal requirements through December 2018 and a portion of its coal requirements through December 2021. Minnesota Power also has coal transportation agreements in place for the delivery of a significant portion of its coal requirements through December 2018. The estimated minimum payments under these supply and transportation agreements is $16.7 million for the remainder of 2018, $1.7 million in 2019, and none thereafter. The costs of fuel and related transportation costs for Minnesota Power’s generation are recoverable from Minnesota Power’s utility customers through the fuel adjustment clause. Leasing Agreements. BNI Energy is obligated to make lease payments for a dragline totaling $2.8 million annually during the lease term, which expires in 2027. BNI Energy has the option at the end of the lease term to renew the lease at fair market value, to purchase the dragline at fair market value, or to surrender the dragline and pay a $3.0 million termination fee. We also lease other properties and equipment under operating lease agreements with a majority of terms expiring by 2024. The aggregate amount of minimum lease payments for all operating leases is $7.1 million for the remainder of 2018, $12.8 million in 2019, $9.5 million in 2020, $7.3 million in 2021, $6.1 million in 2022 and $30.0 million thereafter. Transmission. We continue to make investments in transmission opportunities that strengthen or enhance the transmission grid or take advantage of our geographical location between sources of renewable energy and end users. These include the GNTL, investments to enhance our own transmission facilities, investments in other transmission assets (individually or in combination with others) and our investment in ATC. Great Northern Transmission Line. As a condition of the 250-MW long-term PPA entered into with Manitoba Hydro, construction of additional transmission capacity is required. As a result, Minnesota Power is constructing the GNTL, an approximately 220‑mile 500-kV transmission line between Manitoba and Minnesota’s Iron Range that was proposed by Minnesota Power and Manitoba Hydro in order to strengthen the electric grid, enhance regional reliability and promote a greater exchange of sustainable energy. In 2015, a certificate of need was approved by the MPUC. Based on this approval, Minnesota Power’s portion of the investments and expenditures for the project are eligible for cost recovery under its existing transmission cost recovery rider and are anticipated to be included in future transmission cost recovery filings. (See Note 6. Regulatory Matters.) Also in 2015, the FERC approved our request to recover on construction work in progress related to the GNTL from Minnesota Power’s wholesale customers. In a 2016 order, the MPUC approved the route permit for the GNTL which largely follows Minnesota Power’s preferred route, including the international border crossing, and in 2016, the U.S. Department of Energy issued a presidential permit to cross the U.S.‑Canadian border, which was the final major regulatory approval needed before construction in the U.S. could begin. Site clearing and pre‑construction activities commenced in the first quarter of 2017 with construction expected to be completed in 2020. To date, most of the right-of-way has been cleared while foundation installation and transmission tower construction have commenced. The total project cost in the U.S., including substation work, is estimated to be between $560 million and $710 million, of which Minnesota Power’s portion is expected to be between $300 million and $350 million; the difference will be recovered from a subsidiary of Manitoba Hydro as non-shareholder contributions to capital. Total project costs of $248.8 million have been incurred through June 30, 2018, of which $129.2 million has been recovered from a subsidiary of Manitoba Hydro. Manitoba Hydro must obtain regulatory and governmental approvals related to a new transmission line in Canada known as the Manitoba-Minnesota Transmission Project (MMTP) that will connect with the GNTL. In 2015, Manitoba Hydro submitted the final preferred route and EIS for the MMTP to the Manitoba Conservation and Water Stewardship for siting and environmental approval, which remains pending. In 2016, Manitoba Hydro filed an application with the Canadian National Energy Board (NEB) requesting authorization to construct and operate the MMTP. The NEB determined that Manitoba Hydro’s application was complete in December 2017, and held public hearings in June 2018. The NEB is required to make a decision on the MMTP by March 2019, but is not precluded from making a decision prior to that date. Approval of the Canadian federal cabinet is also required. The MMTP is subject to legal and regulatory challenges which Minnesota Power is actively monitoring. Manitoba Hydro has informed Minnesota Power that it continues to work towards completing the MMTP on schedule. In order to meet the transmission in‑service requirements in PPAs with Minnesota Power, Manitoba Hydro has indicated that it would need to start construction of the MMTP in December 2018. We are unable to predict the outcome of the Canadian regulatory review process, including the timing thereof or whether any onerous conditions may be imposed, or the timing of the completion of the MMTP, including the impact of any delays that may result in construction schedule adjustments. Any significant delays in the MMTP construction schedule may result in Minnesota Power adjusting the GNTL construction schedule and impact the timing of capital expenditures and associated cost recovery under our transmission cost recovery rider. Construction of Manitoba Hydro’s Keeyask hydroelectric generation facility, which will provide the power to be sold under PPAs with Minnesota Power and transmitted on the MMTP and the GNTL, commenced in 2014 and is anticipated to be in service by early 2021. Environmental Matters. Our businesses are subject to regulation of environmental matters by various federal, state and local authorities. A number of regulatory changes to the Clean Air Act, the Clean Water Act and various waste management requirements have been promulgated by both the EPA and state authorities over the past several years. Minnesota Power’s facilities are subject to additional requirements under many of these regulations. Minnesota Power is reshaping its generation portfolio, over time, to reduce its reliance on coal, has installed cost-effective emission control technology, and advocates for sound science and policy during rulemaking implementation. NOTE 13. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) We consider our businesses to be in substantial compliance with currently applicable environmental regulations and believe all necessary permits have been obtained. We anticipate that with many state and federal environmental regulations and requirements finalized, or to be finalized in the near future, potential expenditures for future environmental matters may be material and require significant capital investments. Minnesota Power has evaluated various environmental compliance scenarios using possible outcomes of environmental regulations to project power supply trends and impacts on customers. We review environmental matters on a quarterly basis. Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law and existing technologies. Accruals are adjusted as assessment and remediation efforts progress, or as additional technical or legal information becomes available. Accruals for environmental liabilities are included in the Consolidated Balance Sheet at undiscounted amounts and exclude claims for recoveries from insurance or other third parties. Costs related to environmental contamination treatment and cleanup are expensed unless recoverable in rates from customers. Air. The electric utility industry is regulated both at the federal and state level to address air emissions. Minnesota Power’s generating facilities mainly burn low-sulfur western sub-bituminous coal. All of Minnesota Power’s coal-fired generating facilities are equipped with pollution control equipment such as scrubbers, baghouses and low NOX technologies. Under currently applicable environmental regulations, these facilities are substantially compliant with emission requirements. New Source Review (NSR). In 2014, Minnesota Power reached a settlement with the EPA and entered into a Consent Decree regarding certain Notices of Violation received in 2008 and 2011 that asserted violations of the NSR requirements of the Clean Air Act, which was approved by the U.S. District Court for the District of Minnesota. The Consent Decree provided for, among other requirements, more stringent emissions limits at all affected units, the option of refueling, retrofitting or retiring certain small coal units, and the addition of 200 MW of wind energy. Provisions of the Consent Decree require that, by no later than December 31, 2018, Boswell Units 1 and 2 must be retired, refueled, repowered, or emissions rerouted through existing emission control technology at Boswell. In 2016, Minnesota Power announced that Boswell Units 1 and 2 will be retired in 2018 as part of its EnergyForward strategic plan. We believe that costs to retire Boswell Units 1 and 2 will be eligible for recovery in rates over time, subject to regulatory approval in a rate proceeding. Cross-State Air Pollution Rule (CSAPR). The CSAPR requires certain states in the eastern half of the U.S., including Minnesota, to reduce power plant emissions that contribute to ozone or fine particulate pollution in other states. The CSAPR does not require installation of controls but does require facilities have sufficient allowances to cover their emissions on an annual basis. These allowances are allocated to facilities from each state’s annual budget, and can be bought and sold. Based on our review of the NOx and SO2 allowances issued and pending issuance, we currently expect generation levels and emission rates will result in continued compliance with the CSAPR. Mercury and Air Toxics Standards (MATS) Rule. Under Section 112 of the Clean Air Act, the EPA is required to set emission standards for hazardous air pollutants (HAPs) for certain source categories. The final MATS rule addressed such emissions from coal-fired utility units greater than 25 MW and established categories of HAPs, including mercury, trace metals other than mercury, and acid gases. The EPA established emission limits for these categories of HAPs and work practice standards for the remaining categories. Construction on the project to implement the Boswell Unit 4 mercury emissions reduction plan to position the unit for MATS compliance was completed in 2015. Investments and compliance work previously completed at Boswell Unit 3, including emission reduction investments completed in 2009, meet the requirements of the MATS rule. The conversion of Laskin Units 1 and 2 to operate on natural gas in 2015 positioned those units for MATS compliance. Minnesota Mercury Emissions Reduction Act/Rule. Minnesota Power was required to implement a mercury emissions reduction project for Boswell Unit 4 by December 31, 2018. The Boswell Unit 4 environmental upgrade discussed above (see Mercury and Air Toxics Standards (MATS) Rule) fulfills the requirements of the Minnesota Mercury Emissions Reduction Act. NOTE 13. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) National Ambient Air Quality Standards (NAAQS). The EPA is required to review the NAAQS every five years. If the EPA determines that a state’s air quality is not in compliance with the NAAQS, the state is required to adopt plans describing how it will reduce emissions to attain the NAAQS. Four NAAQS have either recently been revised or are currently proposed for revision, as described below.
Climate Change. The scientific community generally accepts that emissions of GHG are linked to global climate change which creates physical and financial risks. Physical risks could include, but are not limited to: increased or decreased precipitation and water levels in lakes and rivers; increased temperatures; and changes in the intensity and frequency of extreme weather events. These all have the potential to affect the Company’s business and operations. We are addressing climate change by taking the following steps that also ensure reliable and environmentally compliant generation resources to meet our customers’ requirements:
EPA Regulation of GHG Emissions. In 2010, the EPA issued the Prevention of Significant Deterioration (PSD) and Title V Greenhouse Gas Tailoring Rule (Tailoring Rule). The Tailoring Rule establishes permitting thresholds required to address GHG emissions for new facilities, existing facilities that undergo major modifications and other facilities characterized as major sources under the Clean Air Act’s Title V program. For our existing facilities, the rule does not require amending our existing Title V operating permits to include GHG requirements, however, GHG requirements may be added to our existing Title V operating permits by the MPCA as these permits are renewed or amended. NOTE 13. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) In 2014, the U.S. Supreme Court invalidated the aspect of the Tailoring Rule that established higher permitting thresholds for GHG than for other pollutants subject to PSD; however, the court also upheld the EPA’s ability to require best available control technology (BACT) for GHG from sources already subject to regulation under PSD. Minnesota Power’s coal-fired generating facilities are already subject to regulation under PSD, so we anticipate that ultimately PSD for GHG will apply to our facilities, but the timing of the promulgation of a replacement for the Tailoring Rule is uncertain. The PSD applies to existing facilities only when they undertake a major modification that increases emissions. In 2016, the EPA published a proposed rule in the Federal Register to revise its PSD and Title V regulatory provisions concerning GHG emissions. In this proposed rule, the EPA proposes to amend its regulations to clarify that a source’s obligation to obtain a PSD or Title V permit is triggered only by non-GHG pollutants. If the PSD or Title V permitting requirements are triggered by non-GHG, NSR pollutants, then these programs will also apply to the source’s GHG emissions. The proposed rule, as currently written, is not expected to have a material impact on the Title V permitting for current operations. In 2014, the EPA announced a proposed rule under Section 111(d) of the Clean Air Act for existing power plants entitled “Carbon Pollution Emission Guidelines for Existing Stationary Sources: Electric Generating Units”, also referred to as the Clean Power Plan (CPP). The EPA issued the final CPP in 2015, together with a proposed federal implementation plan and a model rule for emissions trading. In 2016, the U.S. Supreme Court issued an order staying the effectiveness of the rule until after the appellate court process is complete. In 2016, the U.S. Court of Appeals for the District of Columbia heard oral arguments and is currently deliberating. If the CPP is upheld at the completion of the appellate process, all of the CPP regulatory deadlines are expected to be reset based on the length of time that the appeals process takes. The EPA is precluded from enforcing the CPP while the U.S. Supreme Court stay is in force; however, the MPCA has been holding a series of meetings on the CPP for educational and planning purposes in the interim. Minnesota Power has been actively involved in these MPCA meetings, and is closely monitoring the appeals process. If upheld, the CPP would establish uniform CO2 emission performance rates for existing fossil fuel-fired and natural gas-fired combined cycle generating units, setting state-specific goals for CO2 emissions from the power sector. State goals were determined based on CPP source-specific performance emission rates and each state’s mix of power plants. The EPA filed a motion with the U.S. Court of Appeals for the District of Columbia Circuit to hold CPP-related litigation in suspension while the EPA is reviewing the rule. In October 2017, the EPA issued a notice of proposed rulemaking, proposing to repeal the CPP. In December 2017, an Advanced Notice of Proposed Rulemaking for a CPP replacement rule was published in the Federal Register. Minnesota Power is currently evaluating the CPP rescission and recent proposal for a CPP replacement rule as it relates to the state of Minnesota as well as its potential impact on the Company. Minnesota has already initiated several measures consistent with those called for under the CPP. Minnesota Power is implementing its EnergyForward strategic plan that provides for significant emission reductions and diversifying its electricity generation mix to include more renewable and natural gas energy. (See Note 6. Regulatory Matters.) We are unable to predict the GHG emission compliance costs we might incur; however, the costs could be material. Minnesota Power would seek recovery of additional costs through a rate proceeding. Water. The Clean Water Act requires NPDES permits be obtained from the EPA (or, when delegated, from individual state pollution control agencies) for any wastewater discharged into navigable waters. We have obtained all necessary NPDES permits, including NPDES storm water permits for applicable facilities, to conduct our operations. Clean Water Act - Aquatic Organisms. In 2014, EPA regulations under Section 316(b) of the Clean Water Act setting standards applicable to cooling water intake structures for the protection of aquatic organisms became effective. The regulations apply to the following facilities: Boswell, Taconite Harbor, Laskin, Rapids Energy Center, Hibbard Renewable Energy Center and portions of the DC transmission line that runs from Center, North Dakota, to Duluth, Minnesota. The Section 316(b) rule will be implemented through NPDES permits issued to covered facilities. No NPDES permits for Minnesota Power facilities have been re-issued containing Section 316(b) requirements since the final rule became effective. Should the MPCA require significant modifications to Minnesota Power’s intake structures, a preliminary assessment indicates that Minnesota Power could incur costs of compliance up to $15 million over the next five years. Minnesota Power would seek recovery of additional costs through a rate proceeding. NOTE 13. COMMITMENTS, GUARANTEES AND CONTINGENCIES (Continued) Environmental Matters (Continued) Steam Electric Power Generating Effluent Guidelines. In 2015, the EPA issued revised federal effluent limit guidelines (ELG) for steam electric power generating stations under the Clean Water Act. It set effluent limits and prescribed BACT for several wastewater streams, including flue gas desulphurization (FGD) water, bottom ash transport water and coal combustion landfill leachate. In September 2017, the EPA announced a two-year postponement of the ELG compliance date of November 1, 2018, to November 1, 2020, while the agency reconsiders the bottom ash transport water and FGD wastewater provisions. The final ELG rule’s potential impact on Minnesota Power operations is primarily at Boswell. Boswell currently discharges bottom ash contact water through its NPDES permit, and also has a closed-loop FGD system that does not discharge, but may do so in the future. Under the existing ELG rule, bottom ash transport water discharge must cease no later than December 31, 2023. Bottom ash contact water will either need to be re-used in a closed-loop process, routed to a FGD scrubber, or the bottom ash handling system will need to be converted to a dry process. If FGD wastewater is discharged in the future, it will require additional wastewater treatment. The ELG rule provision regarding these two waste-streams are being reconsidered and may change prior to November 1, 2020. Efforts have been underway at Boswell to reduce the amount of water discharged and evaluate potential re‑use options in its plant processes. At this time, we cannot estimate what compliance costs we might incur related to these or other potential future water discharge regulations; however, the costs could be material, including costs associated with retrofits for bottom ash handling, pond dewatering, pond closure, and wastewater treatment and re-use. Minnesota Power would seek recovery of additional costs through a rate proceeding. Solid and Hazardous Waste. The Resource Conservation and Recovery Act of 1976 regulates the management and disposal of solid and hazardous wastes. We are required to notify the EPA of hazardous waste activity and, consequently, routinely submit reports to the EPA. Coal Ash Management Facilities. Minnesota Power stores or disposes coal ash at four of its electric generating facilities by the following methods: storing ash in lined onsite impoundments (ash ponds), disposing of dry ash in a lined dry ash landfill, applying ash to land as an approved beneficial use and trucking ash to state permitted landfills. Coal Combustion Residuals from Electric Utilities (CCR). In 2015, the EPA published the final rule regulating CCR as nonhazardous waste under Subtitle D of the Resource Conservation and Recovery Act (RCRA) in the Federal Register. The rule includes additional requirements for new landfill and impoundment construction as well as closure activities related to certain existing impoundments. Costs of compliance for Boswell and Laskin are expected to occur primarily over the next 15 years and be between approximately $65 million and $100 million. The EPA has indicated to Minnesota Power that the Taconite Harbor landfill, which has been idled and has a temporary landfill cover in place, is a CCR unit, based on the EPA’s interpretation of the CCR rule language. Minnesota Power has agreed to post the required CCR information for the Taconite Harbor landfill on Minnesota Power’s website while the CCR issue is resolved. Compliance costs, if any, for CCR at Taconite Harbor cannot be estimated at this time. Minnesota Power would seek recovery of additional costs through a rate proceeding. Minnesota Power continues to work on minimizing costs through evaluation of beneficial re-use and recycling of CCR and CCR‑related waters. In September 2017, the EPA announced its intention to formally reconsider the CCR rule under Subtitle D of the RCRA and on March 15, 2018, published the first phase of the proposed rule revisions in the Federal Register. On July 17, 2018, the EPA finalized revisions to elements of the CCR rule, including extending certain deadlines by two years, the establishment of alternative groundwater protection standards for certain constituents and the potential for risk‑based management options at facilities based on site characteristics. Other Environmental Matters Manufactured Gas Plant Site. We are reviewing and addressing environmental conditions at a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P. SWL&P has been working with the Wisconsin Department of Natural Resources (WDNR) in determining the extent and location of contamination at the site and surrounding properties. In December 2017, the WDNR authorized SWL&P to transition from site investigation into the remedial design process. As of June 30, 2018, we have recorded a liability of approximately $7 million for remediation costs at this site (approximately $8 million as of December 31, 2017), and an associated regulatory asset as we expect recovery of these remediation costs to be allowed by the PSCW. We expect to incur these costs over the next four years. Other Matters. ALLETE Clean Energy. ALLETE Clean Energy’s wind energy facilities have PSAs in place for their entire output and expire in various years between 2018 and 2032. As of June 30, 2018, ALLETE Clean Energy has $16.2 million outstanding in standby letters of credit. U.S. Water Services. As of June 30, 2018, U.S. Water Services has no outstanding standby letters of credit. BNI Energy. As of June 30, 2018, BNI Energy had surety bonds outstanding of $49.9 million and a letter of credit for an additional $0.6 million related to the reclamation liability for closing costs associated with its mine and mine facilities. Although its coal supply agreements obligate the customers to provide for the closing costs, additional assurance is required by federal and state regulations. BNI Energy’s total reclamation liability is currently estimated at $47.5 million. BNI Energy does not believe it is likely that any of these outstanding surety bonds or the letter of credit will be drawn upon. ALLETE Properties. As of June 30, 2018, ALLETE Properties had surety bonds outstanding and letters of credit to governmental entities totaling $8.6 million primarily related to development and maintenance obligations for various projects. The estimated cost of the remaining development work is $6.1 million. ALLETE Properties does not believe it is likely that any of these outstanding surety bonds or letters of credit will be drawn upon. Community Development District Obligations. As of June 30, 2018, we owned 70 percent of the assessable land in the Town Center District (70 percent as of December 31, 2017) and 27 percent of the assessable land in the Palm Coast Park District (33 percent as of December 31, 2017). As of June 30, 2018, ownership levels, our annual assessments related to capital improvement and special assessment bonds for the ALLETE Properties projects within these districts are approximately $1.4 million for Town Center at Palm Coast and $0.6 million for Palm Coast Park. As we sell property at these projects, the obligation to pay special assessments will pass to the new landowners. In accordance with accounting guidance, these bonds are not reflected as debt on our Consolidated Balance Sheet. Legal Proceedings. We are involved in litigation arising in the normal course of business. Also in the normal course of business, we are involved in tax, regulatory and other governmental audits, inspections, investigations and other proceedings that involve state and federal taxes, safety, and compliance with regulations, rate base and cost of service issues, among other things. We do not expect the outcome of these matters to have a material effect on our financial position, results of operations or cash flows. U.S. Water Services is involved in on-going patent defense litigation it brought against a company for infringement of two patents held by U.S. Water Services. As of June 30, 2018, U.S. Water Services has recognized approximately $2 million of patent defense costs as an intangible asset. Management expects that U.S. Water Services will prevail, but in the event of an unfavorable outcome, the patent defense costs would be recognized as an expense in the period of resolution. |
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- Definition The entire disclosure for commitments, contingencies, and guarantees. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| Segment Reporting [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Business Segments [Text Block] | BUSINESS SEGMENTS We present three reportable segments: Regulated Operations, ALLETE Clean Energy and U.S. Water Services. We measure performance of our operations through budgeting and monitoring of contributions to consolidated net income by each business segment. Regulated Operations includes three operating segments which consist of our regulated utilities, Minnesota Power and SWL&P, as well as our investment in ATC. ALLETE Clean Energy is our business focused on developing, acquiring and operating clean and renewable energy projects. U.S. Water Services is our integrated water management company. The ALLETE Clean Energy and U.S. Water Services reportable segments comprise our Energy Infrastructure and Related Services businesses. We also present Corporate and Other which includes two operating segments, BNI Energy, our coal mining operations in North Dakota, and ALLETE Properties, our legacy Florida real estate investment, along with other business development and corporate expenditures, unallocated interest expense, a small amount of non-rate base generation, approximately 4,000 acres of land in Minnesota, and earnings on cash and investments. NOTE 14. BUSINESS SEGMENTS (Continued)
NOTE 14. BUSINESS SEGMENTS (Continued)
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- Definition The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||
| Cash and Cash Equivalents, Policy [Policy Text Block] | We consider all investments purchased with original maturities of three months or less to be cash equivalents. |
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| Inventories – Net [Policy Text Block] | Inventories are stated at the lower of cost or net realizable value. Inventories in our Regulated Operations segment are carried at an average cost or first-in, first-out basis. Inventories in our U.S. Water Services and ALLETE Clean Energy segments, and Corporate and Other businesses are carried at an average cost, first-in, first-out or specific identification basis. |
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| Subsequent Events [Policy Text Block] | The Company performed an evaluation of subsequent events for potential recognition and disclosure through the date of the financial statements issuance. |
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| Revenue Recognition, Policy [Policy Text Block] | Revenue is recognized upon transfer of control of promised goods or services to our customers in an amount that reflects the consideration we expect to receive in exchange for those products or services. Revenue is recognized net of allowance for returns and any taxes collected from customers, which are subsequently remitted to the appropriate governmental authorities. We account for shipping and handling activities that occur after the customer obtains control of goods as a cost rather than an additional performance obligation thereby recognizing revenue at time of shipment and accruing shipping and handling costs when control transfers to our customers. We have a right to consideration from our customers in an amount that corresponds directly with the value to the customer for our performance completed to date; therefore, we may recognize revenue in the amount to which we have a right to invoice. |
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| Revenue Recognition for Alternative Revenue Programs, Policy [Policy Text Block] | Alternative Programs includes revenue that is driven by factors outside of our regulated entities’ control or as a result of the achievement of certain objectives, such as CIP financial incentives. This revenue is accounted for in accordance with the accounting standards for alternative revenue programs which allow for the recognition of revenue under an alternative revenue program if the program is established by an order from the utility’s regulatory commission, the order allows for automatic adjustment of future rates, the amount of revenue recognized is objectively determinable and probable of recovery, and the revenue will be collected within 24 months following the end of the annual period in which it is recognized. CIP financial incentives are recognized in the period in which the MPUC approves the filing, which is typically mid-year. |
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| New Accounting Standards [Policy Text Block] | New Accounting Pronouncements. Recently Adopted Pronouncements Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. In February 2018, the FASB issued an update allowing for a one-time reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the enactment of the TCJA. With the enactment of the new federal tax rates in 2017, entities were required to adjust deferred tax assets and liabilities to reflect the lower federal rate with the effect of this reduction impacting income from continuing operations in the period of enactment, even in instances where the related income tax effects of items were originally recognized in other comprehensive income. As such, companies were left with stranded tax effects in accumulated other comprehensive income that did not reflect the appropriate tax rate. This guidance is effective in the first quarter of 2019 with early adoption permitted. The Company elected to early adopt this guidance in the first quarter of 2018 which resulted in a reduction of $5.7 million to Accumulated Other Comprehensive Loss and a corresponding increase to Retained Earnings for the reclassification of the stranded income tax effects. Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. In March 2017, the FASB issued an accounting standard update to improve the presentation of net periodic pension and postretirement benefit costs. Under the guidance, an entity is required to present the service cost component of the net periodic benefit cost in the same income statement line as other employee compensation costs arising from services rendered during the period. The guidance also allows only the service cost component of the periodic cost to be eligible for capitalization on a prospective basis. The other components of net periodic expense must be presented separately from the line item that includes the service cost and must be excluded from the operating income subtotal. The Company adopted the guidance in the first quarter of 2018 and retrospectively adjusted the presentation of the service cost component and the other components of net periodic costs in the Consolidated Statement of Income. The retrospective adjustments for the quarter and six months ended June 30, 2017, were as follows: Operating and Maintenance increased $1.0 million and $2.1 million, respectively, Cost of Sales – Non-utility remained unchanged and decreased $0.1 million, respectively, resulting in an increase of $1.0 million and $2.0 million, respectively to Other Income (Expense) – Other. There was no impact to net income as a result of adoption. Financial Instruments. In 2016, the FASB issued an accounting standard update which requires entities to measure equity investments at fair value and recognize any changes in fair value in net income unless the investments qualify for the practicability exception. The practicability exception will be available for equity investments that do not have readily determinable fair values. The update was adopted by the Company in the first quarter of 2018 which resulted in a cumulative-effect transition adjustment reducing Retained Earnings by $0.1 million, including the tax effect, for the previously unrealized loss on available-for-sale equity securities in Accumulated Other Comprehensive Loss as of December 31, 2017. Classification of Certain Cash Receipts and Cash Payments. In 2016, the FASB issued an accounting standard update which addressed the following eight specific cash flow issues: debt prepayment or debt extinguishment costs; settlement of zero‑coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies (including bank-owned life insurance policies); distributions received from equity method investees; beneficial interests in securitization transactions; and separately identifiable cash flows and application of the predominance principle. The amendments of this update were adopted by the Company in the first quarter of 2018. There was no impact to the Consolidated Statement of Cash Flows as a result of adoption. Statement of Cash Flows: Restricted Cash. In 2016, the FASB issued an accounting standard update related to the presentation of restricted cash in the Company’s Consolidated Statement of Cash Flows. The update requires that the Consolidated Statement of Cash Flows explain the change during the period in cash, cash equivalents and restricted cash. Restricted cash should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the Consolidated Statement of Cash Flows. This guidance update was adopted by the Company in the first quarter of 2018 and was applied retrospectively to the periods presented in the Consolidated Statement of Cash Flows which resulted in a net increase in cash from financing activities of $1.5 million for the six months ended June 30, 2017. Additional disclosure, including a reconciliation of the beginning-of-period and end-of-period cash on hand to the statement of cash flows, is included in this note. (See Cash, Cash Equivalents and Restricted Cash.) NOTE 1. OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES (Continued) New Accounting Pronouncements (Continued) Revenue from Contracts with Customers. In 2014, the FASB issued amended revenue recognition guidance that clarifies the principles for recognizing revenue from contracts with customers by providing a single comprehensive model to determine the measurement of revenue and timing of recognition. The guidance requires an entity to recognize revenue in a manner that depicts the transfer of goods or services to customers in an amount that reflects the consideration to which an entity expects to be entitled to in exchange for those goods or services. The guidance requires expanded disclosures relating to the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Additionally, qualitative and quantitative disclosures regarding customer contracts, significant judgments and changes in those judgments, and the assets recognized from the costs to obtain or fulfill a contract are required. The Company adopted this accounting guidance in the first quarter of 2018 and elected to apply the modified retrospective method of adoption to all contracts as of the date of initial application. The financial impact to the consolidated financial statements as a result of adoption of the new standard is immaterial. Based on the nature of the contracts with our customers and our related performance obligations which transfer control, a $0.5 million after-tax cumulative‑effect transition adjustment was made to increase the opening balance of Retained Earnings. We have included additional disclosures in the notes to the consolidated financial statements including additional information on the Company’s revenue streams and related performance obligations required to be satisfied in order to recognize revenue. (See Revenue Recognition.) Practical Expedients The following practical expedients were used by the Company as part of the adoption of the new revenue recognition guidance:
Recently Issued Pronouncements Simplifying the Test for Goodwill Impairment. In January 2017, the FASB issued updated guidance which simplifies the measurement of goodwill impairment by removing step two of the goodwill impairment test that requires the determination of the fair value of individual assets and liabilities of a reporting unit. The updated guidance requires goodwill impairment to be measured as the amount by which a reporting unit’s carrying value exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. This guidance is effective for the Company beginning in the first quarter of 2020, with early adoption permitted on a prospective basis. Leases. In 2016, the FASB issued an accounting standard update which revises the existing guidance for leases. Under the revised guidance, lessees will be required to recognize a “right-of-use” asset and a lease liability for all leases with a term greater than 12 months. The new standard also requires additional quantitative and qualitative disclosures by lessees and lessors to enable users of the financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. The accounting for leases by lessors and the recognition, measurement, and presentation of expenses and cash flows from leases are not expected to significantly change as a result of the new guidance. We expect to make approximately $80 million in minimum lease payments due in future years (undiscounted). The revised guidance is effective for the Company beginning in the first quarter of 2019 with early adoption permitted. We are currently evaluating the impact of the revised lease guidance on our Consolidated Financial Statements. |
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| Land Inventory [Policy Text Block] | We account for our available-for-sale securities portfolio in accordance with the guidance for certain investments in debt and equity securities. |
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| Available-for-sale Investments [Policy Text Block] | We account for our available-for-sale securities portfolio in accordance with the guidance for certain investments in debt and equity securities. |
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| Acquisitions [Policy Text Block] | The acquisition was accounted for as a business combination and the purchase price was allocated based on the estimated fair values of the assets acquired and the liabilities assumed at the date of acquisition. |
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| Fair Value Measurement [Policy Text Block] | We utilize market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and the risks inherent in the inputs to the valuation technique. These inputs can be readily observable, market corroborated or generally unobservable. We primarily apply the market approach for recurring fair value measurements and endeavor to utilize the best available information. Accordingly, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs, which are used to measure fair value, are prioritized through the fair value hierarchy. Non-financial assets such as equity method investments, goodwill, intangible assets, land inventory, and property, plant and equipment are measured at fair value when there is an indicator of impairment and recorded at fair value only when an impairment is recognized. Management analyzes the fair value of the contingent liability on a quarterly basis and makes adjustments as appropriate. |
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| Regulatory Assets and Liabilities [Policy Text Block] | Our regulated utility operations are subject to accounting guidance for the effect of certain types of regulation. Regulatory assets represent incurred costs that have been deferred as they are probable for recovery in customer rates. Regulatory liabilities represent obligations to make refunds to customers and amounts collected in rates for which the related costs have not yet been incurred. The Company assesses quarterly whether regulatory assets and liabilities meet the criteria for probability of future recovery or deferral. No regulatory assets or liabilities are currently earning a return. The recovery, refund or credit to rates for these regulatory assets and liabilities will occur over the periods either specified by the applicable regulatory authority or over the corresponding period related to the asset or liability. |
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| Equity Method Investments [Policy Text Block] | We account for our investment in ATC under the equity method of accounting. |
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| Income Tax [Policy Text Block] | The Company's tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items arising in that quarter. In each quarter, the Company updates its estimate of the annual effective tax rate, and if the estimated annual effective tax rate changes, the Company would make a cumulative adjustment in that quarter. |
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| Uncertain Tax Positions [Policy Text Block] | The unrecognized tax benefit amounts have been presented as reductions to the tax benefits associated with NOL and tax credit carryforwards on the Consolidated Balance Sheet. |
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| Earnings Per Share [Policy Text Block] | We compute basic earnings per share using the weighted average number of shares of common stock outstanding during each period. The difference between basic and diluted earnings per share, if any, arises from outstanding stock options, non-vested restricted stock units and performance share awards granted under our Executive Long-Term Incentive Compensation Plan. For the quarter and six months ended June 30, 2018, and 2017, no options to purchase shares of ALLETE common stock were excluded from the computation of diluted earnings per share. |
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| Power Purchase Agreements [Policy Text Block] | Our long-term PPAs have been evaluated under the accounting guidance for variable interest entities. We have determined that either we have no variable interest in the PPAs or, where we do have variable interests, we are not the primary beneficiary; therefore, consolidation is not required. These conclusions are based on the fact that we do not have both control over activities that are most significant to the entity and an obligation to absorb losses or receive benefits from the entity’s performance. Our financial exposure relating to these PPAs is limited to our capacity and energy payments. |
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| Environmental Accruals [Policy Text Block] | We review environmental matters on a quarterly basis. Accruals for environmental matters are recorded when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated based on current law and existing technologies. Accruals are adjusted as assessment and remediation efforts progress, or as additional technical or legal information becomes available. Accruals for environmental liabilities are included in the Consolidated Balance Sheet at undiscounted amounts and exclude claims for recoveries from insurance or other third parties. Costs related to environmental contamination treatment and cleanup are expensed unless recoverable in rates from customers. |
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| Business Segments [Policy Text Block] | We present three reportable segments: Regulated Operations, ALLETE Clean Energy and U.S. Water Services. We measure performance of our operations through budgeting and monitoring of contributions to consolidated net income by each business segment. |
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- Definition Disclosure of accounting policy for completed business combinations (purchase method, acquisition method or combination of entities under common control). This accounting policy may include a general discussion of the purchase method or acquisition method of accounting (including for example, the treatment accorded contingent consideration, the identification of assets and liabilities, the purchase price allocation process, how the fair values of acquired assets and liabilities are determined) and the entity's specific application thereof. An entity that acquires another entity in a leveraged buyout transaction generally discloses the accounting policy followed by the acquiring entity in determining the basis used to value its interest in the acquired entity, and the rationale for that accounting policy. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for cash and cash equivalents, including the policy for determining which items are treated as cash equivalents. Other information that may be disclosed includes (1) the nature of any restrictions on the entity's use of its cash and cash equivalents, (2) whether the entity's cash and cash equivalents are insured or expose the entity to credit risk, (3) the classification of any negative balance accounts (overdrafts), and (4) the carrying basis of cash equivalents (for example, at cost) and whether the carrying amount of cash equivalents approximates fair value. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for consolidation to describe the significant judgments and assumptions made in determining whether a variable interest held by the entity requires the variable interest entity to be consolidated and (or) disclose information about its involvement with the variable interest entity; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; and the significant factors considered and judgments made in determining that the power to direct the activities that significantly impact the economic performance of the variable interest entity are shared (as defined). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for computing basic and diluted earnings or loss per share for each class of common stock and participating security. Addresses all significant policy factors, including any antidilutive items that have been excluded from the computation and takes into account stock dividends, splits and reverse splits that occur after the balance sheet date of the latest reporting period but before the issuance of the financial statements. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for obligations that resulted from improper or other-than normal operation of a long-lived asset in the past. This accounting policy may address (1) whether the related remediation costs are expensed or capitalized, (2) whether the obligation is measured on a discounted basis, (3) the event, situation, or set of circumstances that generally triggers recognition of loss contingencies arising from the entity's environmental remediation-related obligations, and (4) the timing of recognition of any recoveries. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for equity method of accounting for investments and other interests. Investment includes, but is not limited to, unconsolidated subsidiary, corporate joint venture, noncontrolling interest in real estate venture, limited partnership, and limited liability company. Information includes, but is not limited to, ownership percentage, reason equity method is or is not considered appropriate, and accounting policy election for distribution received. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for fair value measurements of financial and non-financial assets, liabilities and instruments classified in shareholders' equity. Disclosures include, but are not limited to, how an entity that manages a group of financial assets and liabilities on the basis of its net exposure measures the fair value of those assets and liabilities. No definition available.
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- Definition Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Disclosure of accounting policy for tax positions taken in the tax return filed or to be filed for which it is more likely than not that the tax position will not be sustained upon examination by taxing authorities and other types of contingencies related to income taxes. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of inventory accounting policy for inventory classes, including, but not limited to, basis for determining inventory amounts, methods by which amounts are added and removed from inventory classes, loss recognition on impairment of inventories, and situations in which inventories are stated above cost. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for investment classified as marketable security. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy pertaining to new accounting pronouncements that may impact the entity's financial reporting. Includes, but is not limited to, quantification of the expected or actual impact. No definition available.
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- References No definition available.
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- Definition Disclosure of accounting policy for public utilities. Examples include a discussion about the scope criteria and appropriateness for and extent of the application of generally accepted accounting principles related to accounting for the effects of certain types of regulation (may include identification of specific business units). Other examples of the disclosures may include: descriptions of the form and economic effects of regulation (for example, but not limited to, recording of regulatory assets and liabilities to the rate setting process); statement about periodic assessments of periodic assessments of generally accepted accounting principles related to accounting for the effects of certain types of regulation; information regarding amortization of and return on regulatory assets and liabilities, including the remaining amounts and recovery or settlement periods; accounting for changes to recovery estimates; AFUDC, plant abandonment's and plant disallowances. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for real estate held for development or sale. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for revenue recognition related to alternative revenue programs. The major alternative revenue programs can generally be segregated into two categories, programs that adjust billings for the effects of weather abnormalities or broad external factors or to compensate the utility for demand-side management initiatives (for example, no-growth plans and similar conservation efforts); and programs that provide for additional billings (incentive awards) if the utility achieves certain objectives, such as reducing costs, reaching specified milestones, or demonstratively improving customer service. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for revenue recognition. If the entity has different policies for different types of revenue transactions, the policy for each material type of transaction is generally disclosed. If a sales transaction has multiple element arrangements (for example, delivery of multiple products, services or the rights to use assets) the disclosure may indicate the accounting policy for each unit of accounting as well as how units of accounting are determined and valued. The disclosure may encompass important judgment as to appropriateness of principles related to recognition of revenue. The disclosure also may indicate the entity's treatment of any unearned or deferred revenue that arises from the transaction. Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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- Definition Disclosure of accounting policy for segment reporting. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Disclosure of accounting policy for reporting subsequent events. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Operations and Significant Accounting Policies (Tables) |
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| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cash, Cash Equivalents and Restricted Cash [Table Text Block] | The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheet that aggregate to the amount presented in the Consolidated Statement of Cash Flows. During the first quarter of 2018, the Company updated the presentation of its Consolidated Statement of Cash Flows to include restricted cash with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the Consolidated Statement of Cash Flows. (See Recently Adopted Pronouncements - Statement of Cash Flows: Restricted Cash.)
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| Other Non-Current Assets [Table Text Block] |
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| Other Current Liabilities [Table Text Block] |
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| Supplemental Statement of Cash Flows Information [Table Text Block] | Supplemental Statement of Cash Flows Information.
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- Definition Tabular disclosure of the carrying amount as of the balance sheet date of merchandise, goods, commodities, or supplies held for future sale or to be used in manufacturing, servicing or production process. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Tabular disclosure of noncurrent assets. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Investments (Tables) |
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| Other Investments [Table Text Block] |
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- Definition A table of investments, shown as a text block. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- References No definition available.
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Acquisitions (Table) |
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| Schedule of Business Acquisitions [Table Text Block] |
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- Definition Tabular disclosure of a material business combination completed during the period, including background, timing, and recognized assets and liabilities. This table does not include leveraged buyouts. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Goodwill and Intangible Assets (Tables) |
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| Schedule of Intangible Assets [Table Text Block] | Balances of intangible assets, net, excluding goodwill as of June 30, 2018, are as follows:
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- Definition Tabular disclosure of goodwill and intangible assets, which may be broken down by segment or major class. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Fair Value (Tables) |
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| Fair Value Disclosures [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Recurring Fair Value Measures [Table Text Block] |
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| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] |
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| Financial Instruments [Table Text Block] |
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- Definition Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition Tabular disclosure of the fair value measurement of liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets), and gains or losses recognized in other comprehensive income (loss) and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs) by class of liability. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Regulatory Matters (Tables) |
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Jun. 30, 2018 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Regulated Operations [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Regulatory Assets and Liabilities [Table Text Block] |
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- References No definition available.
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- Definition The entire disclosure for detailed information about regulatory assets and liabilities, including current and noncurrent assets created when regulatory agencies permit the deferral of costs to the balance sheet that would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues, as well as current and noncurrent liabilities created when regulatory agencies permit. No definition available.
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Investment in ATC (Tables) |
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Jun. 30, 2018 | |||||||||||||||||||||||||||||||||||||||||
| Equity Method Investments and Joint Ventures [Abstract] | |||||||||||||||||||||||||||||||||||||||||
| ALLETE's Investment in ATC [Table Text Block] |
(a) Amortization related to the impact of the remeasurement of deferred income tax assets and liabilities resulting from the TCJA. |
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- Definition Tabular disclosure of equity method investments including, but not limited to, name of each investee or group of investments, percentage ownership, difference between recorded amount of an investment and the value of the underlying equity in the net assets, and summarized financial information. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Short-Term and Long-Term Debt (Tables) |
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Jun. 30, 2018 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Debt Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Schedule of Short-Term and Long-Term Debt [Table Text Block] | The following tables present the Company’s short-term and long-term debt as of June 30, 2018, and December 31, 2017:
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- Definition Tabular disclosure of information pertaining to short-term and long-debt instruments or arrangements, including but not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation. No definition available.
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Income Tax Expense (Tables) |
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| Income Tax Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Income Tax Expense [Table Text Block] |
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| Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Table Text Block] |
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- Definition Tabular disclosure of the components of income tax expense attributable to continuing operations for each year presented including, but not limited to: current tax expense (benefit), deferred tax expense (benefit), investment tax credits, government grants, the benefits of operating loss carryforwards, tax expense that results from allocating certain tax benefits either directly to contributed capital or to reduce goodwill or other noncurrent intangible assets of an acquired entity, adjustments of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity, and adjustments of the beginning-of-the-year balances of a valuation allowance because of a change in circumstances that causes a change in judgment about the realizability of the related deferred tax asset in future years. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Earnings Per Share and Common Stock (Tables) |
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| Earnings Per Share [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block] |
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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Pension and Other Postretirement Benefit Plans (Tables) |
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| Retirement Benefits [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Components of Net Periodic Benefit Expense (Income) [Table Text Block] |
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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Business Segments (Tables) |
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| Segment Reporting [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Business Segments [Table Text Block] |
NOTE 14. BUSINESS SEGMENTS (Continued)
|
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| X | ||||||||||
- Definition Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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Operations and Significant Accounting Policies (Details) - USD ($) $ in Millions |
Jun. 30, 2018 |
Dec. 31, 2017 |
Jun. 30, 2017 |
Dec. 31, 2016 |
|||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cash, Cash Equivalents and Restricted Cash [Abstract] | |||||||||||||||||||||
| Cash and Cash Equivalents | $ 121.9 | $ 98.9 | $ 84.2 | $ 27.5 | |||||||||||||||||
| Restricted Cash included in Prepayments and Other | 2.3 | 2.6 | 3.7 | 2.2 | |||||||||||||||||
| Restricted Cash included in Other Non-Current Assets | 8.6 | 8.6 | 8.6 | 8.6 | |||||||||||||||||
| Total Cash, Cash Equivalents and Restricted Cash | 132.8 | 110.1 | $ 96.5 | $ 38.3 | |||||||||||||||||
| Inventories – Net [Abstract] | |||||||||||||||||||||
| Fuel | [1] | 31.4 | 34.8 | ||||||||||||||||||
| Materials and Supplies | 44.3 | 46.5 | |||||||||||||||||||
| Construction of Wind Energy Facility | [2] | 54.1 | 0.0 | ||||||||||||||||||
| Raw Materials | 3.0 | 2.8 | |||||||||||||||||||
| Work in Progress | 4.4 | 4.2 | |||||||||||||||||||
| Finished Goods | 9.1 | 8.3 | |||||||||||||||||||
| Reserve for Obsolescence | (0.9) | (0.7) | |||||||||||||||||||
| Total Inventories – Net | 145.4 | 95.9 | |||||||||||||||||||
| Other Non-Current Assets [Abstract] | |||||||||||||||||||||
| Contract Assets | [3] | 30.9 | 31.6 | ||||||||||||||||||
| Finance Receivable | 10.9 | 11.0 | |||||||||||||||||||
| Other | 63.2 | 65.1 | |||||||||||||||||||
| Total Other Non-Current Assets | 105.0 | 107.7 | |||||||||||||||||||
| Other Current Liabilites [Abstract] | |||||||||||||||||||||
| Provision for Interim Rate Refund | [4] | 32.5 | 0.0 | ||||||||||||||||||
| Contract Liabilities | [5] | 24.3 | 8.7 | ||||||||||||||||||
| PSAs | 18.4 | 24.5 | |||||||||||||||||||
| Provision for Tax Reform Refunds | [6] | 6.7 | 0.0 | ||||||||||||||||||
| Contingent Consideration - Current | [7] | 5.6 | 0.0 | ||||||||||||||||||
| Other | 41.0 | 50.0 | |||||||||||||||||||
| Total Other Current Liabilities | 128.5 | 83.2 | |||||||||||||||||||
| Other Non-Current Liabilities [Abstract] | |||||||||||||||||||||
| Asset Retirement Obligation | 143.2 | 122.7 | |||||||||||||||||||
| PSAs | 83.1 | 89.5 | |||||||||||||||||||
| Contingent Consideration - Non-current | [8] | 0.0 | 5.4 | ||||||||||||||||||
| Other | 48.1 | 49.5 | |||||||||||||||||||
| Total Other Non-Current Liabilities | $ 274.4 | $ 267.1 | |||||||||||||||||||
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| X | ||||||||||
- Definition The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a current liability. No definition available.
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| X | ||||||||||
- Definition The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a noncurrent liability. No definition available.
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| X | ||||||||||
- Definition Provision for Interim Rate Refund No definition available.
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| X | ||||||||||
- Definition Provision for Tax Reform Refunds No definition available.
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| X | ||||||||||
- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled within one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as noncurrent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Carrying amount as of the balance sheet date of coal, which is a combustible rock or minerals which are extracted from the ground and used as fuel. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount before valuation and LIFO reserves of raw materials expected to be sold, or consumed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of valuation reserve for inventory. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of expenses incurred but not yet paid classified as other, due after one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of other miscellaneous assets expected to be realized or consumed after one year or normal operating cycle, if longer. No definition available.
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| X | ||||||||||
- Definition Amount of noncurrent assets classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount before valuation and LIFO reserves of other inventory expected to be sold, or consumed within one year or operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of cash restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Operations and Significant Accounting Policies - Supplemental Statement of Cash Flows Information (Details) - USD ($) $ in Millions |
6 Months Ended | |||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
|||
| Supplemental Cash Flow Information [Abstract] | ||||
| Cash Paid for Interest – Net of Amounts Capitalized | $ 33.0 | $ 32.5 | ||
| Noncash Investing and Financing Activities [Abstract] | ||||
| Decrease in Accounts Payable for Capital Additions to Property, Plant and Equipment | (39.4) | (0.4) | ||
| Reclassification of Property, Plant and Equipment to Inventory | [1] | 46.3 | 0.0 | |
| Capitalized Asset Retirement Costs | 20.8 | 19.7 | ||
| AFUDC–Equity | 0.5 | 0.4 | ||
| ALLETE Common Stock Contributed to the Pension Plans | $ 0.0 | $ 13.5 | ||
| ||||
| X | ||||||||||
- Definition Increase (Decrease) in Accounts Payable for Capital Additions to Property, Plant and Equipment No definition available.
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| X | ||||||||||
- Definition Reclassification of Property, Plant and Equipment to Inventory No definition available.
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the capitalized cost of equity (based on assumed rate of return) and / or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. As a result of this capitalization, net income is increased. This element pertains to certain regulated industries, such as public utilities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the carrying amount of asset retirement obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan. No definition available.
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Contract Serving Requirement No definition available.
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| X | ||||||||||
- Definition Large Power Customer Contracts No definition available.
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| X | ||||||||||
- Definition Length of Notice Required to Terminate Contract No definition available.
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| X | ||||||||||
- Definition Number of Customers No definition available.
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| X | ||||||||||
- Definition Percentage of Total Regulated Utility kWh Sales No definition available.
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| X | ||||||||||
- Definition Revenue Collection Period Following the Annual Period it is Recognized No definition available.
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| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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| X | ||||||||||
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| X | ||||||||||
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| X | ||||||||||
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| X | ||||||||||
- Definition Description of payment terms in contract with customer. Includes, but is not limited to, timing of payment, existence of financing component, variability of consideration and constraint on variable consideration. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of transaction price allocated to performance obligation that has not been recognized as revenue. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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| X | ||||||||||
- Definition Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
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| X | ||||||||||
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Operations and Significant Accounting Policies - Revenue - Assets Recognized From the Costs to Obtain a Contract with a Customer (Details) - USD ($) $ in Millions |
6 Months Ended | ||||
|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
|||
| Revenue from Contract with Customer [Abstract] | |||||
| Contract Assets | [1] | $ 30.9 | $ 31.6 | ||
| Contract Asset Non-Cash Amortization | $ 1.3 | $ 0.6 | |||
| |||||
| X | ||||||||||
- Definition Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as noncurrent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. No definition available.
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| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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| X | ||||||||||
- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The amount of a reclassification adjustment made to prior period financial statement amounts. No definition available.
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| X | ||||||||||
- Details
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| X | ||||||||||
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| X | ||||||||||
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Operations and Significant Accounting Policies - Reclassification of Prior Income Statement (Details) - Accounting Standards Update 2017-07 [Member] - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended |
|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2017 |
|
| Operating and Maintenance [Member] | ||
| Reclassification of Prior Income Statement [Line Items] | ||
| Prior Period Reclassification Amount | $ 1.0 | $ 2.1 |
| Other Income (Expense) [Member] | ||
| Reclassification of Prior Income Statement [Line Items] | ||
| Prior Period Reclassification Amount | $ 1.0 | $ 2.0 |
| X | ||||||||||
- Definition [Line Items] for Schedule of prior period reclassification adjustments to conform the presentation of prior period financial statements with the presentation in the current period. No definition available.
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| X | ||||||||||
- Definition The amount of a reclassification adjustment made to prior period financial statement amounts. No definition available.
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| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
Investments (Details) - USD ($) $ in Millions |
Jun. 30, 2018 |
Dec. 31, 2017 |
|||
|---|---|---|---|---|---|
| Investments [Abstract] | |||||
| ALLETE Properties | $ 25.9 | $ 26.4 | |||
| Available-for-sale Securities | 21.4 | [1] | 19.1 | ||
| Cash Equivalents | 1.5 | 3.8 | |||
| Other | 3.7 | 3.8 | |||
| Total Other Investments | 52.5 | $ 53.1 | |||
| Available-for-sale Corporate and Governmental Debt Securities, Maturities [Abstract] | |||||
| One Year or Less | 1.1 | ||||
| One Year to Less Than Three Years | 3.9 | ||||
| Three Years to Less Than Five Years | 2.5 | ||||
| Five or More Years | $ 1.1 | ||||
| |||||
| X | ||||||||||
- Definition Amount of available-for-sale debt securities at fair value maturing in after the fifth fiscal year following the latest fiscal year (maturing in five years or more). No definition available.
|
| X | ||||||||||
- Definition Amount of available-for-sale debt securities at fair value maturing after the first fiscal year through the third fiscal year following the latest fiscal year (maturing in more than one year to less than three years). No definition available.
|
| X | ||||||||||
- Definition Amount of available-for-sale debt securities at fair value maturing after the third fiscal year through the fifth fiscal year following the latest fiscal year (maturing in three years to less than five years). No definition available.
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income. No definition available.
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of long-term investments classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of noncurrent assets that are pledged or subject to withdrawal restrictions, classified as other. No definition available.
|
| X | ||||||||||
- Definition Amount of real estate investments, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; (7) other real estate investments; (8) real estate joint ventures; and (9) unconsolidated real estate and other joint ventures not separately presented. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
Acquisitions (Details) |
6 Months Ended | |
|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Business Combinations [Abstract] | ||
| Reason for Business Acquisitions | The following acquisition is consistent with ALLETE’s stated strategy of investing in energy infrastructure and related services businesses to complement its regulated businesses, balance exposure to business cycles and changing demand, and provide potential long-term earnings growth. | The following acquisitions are consistent with ALLETE’s stated strategy of investing in energy infrastructure and related services businesses to complement its regulated businesses, balance exposure to business cycles and changing demand, and provide potential long-term earnings growth. |
| X | ||||||||||
- Definition This element represents a description of the primary reason for the business combination which may consist of general categories such as top-line growth, synergistic benefits, market share, and diversification and the more detailed factors that might apply. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
Acquisitions - Tonka Water (Details) - USD ($) $ in Millions |
Sep. 01, 2017 |
Jun. 30, 2018 |
Dec. 31, 2017 |
|||||
|---|---|---|---|---|---|---|---|---|
| Assets Acquired [Abstract] | ||||||||
| Goodwill | $ 148.5 | $ 148.3 | ||||||
| Tonka Water [Member] | ||||||||
| Business Acquisition [Line Items] | ||||||||
| Percentage of Voting Interests Acquired | 100.00% | |||||||
| Name of Acquired Entity | Tonka Water | |||||||
| Total Consideration | $ 19.2 | |||||||
| Cash Payment to Acquire Business | 19.0 | |||||||
| Working Capital Adjustment Paid in the Fourth Quarter 2017 | 0.2 | |||||||
| Assets Acquired [Abstract] | ||||||||
| Accounts Receivable | 5.1 | |||||||
| Other Current Assets | 5.1 | |||||||
| Trade Names | [1] | 0.9 | ||||||
| Goodwill | [1],[2] | 16.9 | ||||||
| Other Non-Current Assets | 0.2 | |||||||
| Total Assets Acquired | 28.2 | |||||||
| Liabilities Assumed [Abstract] | ||||||||
| Current Liabilities | 9.0 | |||||||
| Total Liabilities Assumed | 9.0 | |||||||
| Net Identifiable Assets Acquired | 19.2 | |||||||
| Tax Deductible Goodwill | $ 4.1 | |||||||
| ||||||||
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Name of the acquired entity. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Percentage of voting equity interests acquired at the acquisition date in the business combination. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of assets acquired at the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of intangible assets, excluding goodwill, acquired at the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of liabilities assumed at the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Details
|
Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
|
| Goodwill and Intangible Assets Disclosure [Abstract] | |||||
| Goodwill | $ 148.5 | $ 148.5 | $ 148.3 | ||
| Amortization of Intangible Assets | $ 1.3 | $ 1.4 | $ 2.7 | $ 2.8 | |
| X | ||||||||||
- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Beginning Balance | $ 61.0 | |||||||
| Additions | 2.4 | |||||||
| Amortization | $ (1.3) | $ (1.4) | (2.7) | $ (2.8) | ||||
| Ending Balance | 60.7 | 60.7 | ||||||
| Accumulated Amortization | 17.5 | 17.5 | $ 14.8 | |||||
| Estimated Annual Amortization Expense for Definite-Lived Intangible Assets [Abstract] | ||||||||
| Remainder of 2018 | 2.8 | 2.8 | ||||||
| 2019 | 5.2 | 5.2 | ||||||
| 2020 | 5.0 | 5.0 | ||||||
| 2021 | 4.9 | 4.9 | ||||||
| 2022 | 4.6 | 4.6 | ||||||
| Thereafter | 38.2 | 38.2 | ||||||
| Intangible Assets Acquired | 2.4 | |||||||
| Intangible Assets [Abstract] | ||||||||
| Total Intangible Assets | 77.3 | 77.3 | $ 77.6 | |||||
| Total Intangible Assets, Amortization | (1.3) | $ (1.4) | $ (2.7) | $ (2.8) | ||||
| Weighted Average [Member] | ||||||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Remaining Useful Life (Years) | 18 years | |||||||
| Trademarks and Trade Names [Member] | ||||||||
| Indefinite-Lived Intangible Assets [Roll Forward] | ||||||||
| Beginning Balance | $ 16.6 | |||||||
| Additions | 0.0 | |||||||
| Ending Balance | 16.6 | 16.6 | ||||||
| Customer Relationships [Member] | ||||||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Beginning Balance | 54.7 | |||||||
| Additions | 0.2 | |||||||
| Amortization | (2.1) | |||||||
| Ending Balance | 52.8 | $ 52.8 | ||||||
| Remaining Useful Life (Years) | 20 years | |||||||
| Intangible Assets [Abstract] | ||||||||
| Total Intangible Assets, Amortization | $ (2.1) | |||||||
| Developed Technology and Other [Member] | ||||||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Beginning Balance | [1] | 6.3 | ||||||
| Additions | [1] | 2.2 | ||||||
| Amortization | [1] | (0.6) | ||||||
| Ending Balance | [1] | $ 7.9 | 7.9 | |||||
| Intangible Assets [Abstract] | ||||||||
| Total Intangible Assets, Amortization | [1] | $ (0.6) | ||||||
| Developed Technology and Other [Member] | Minimum [Member] | ||||||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Remaining Useful Life (Years) | 1 year | |||||||
| Developed Technology and Other [Member] | Maximum [Member] | ||||||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Remaining Useful Life (Years) | 11 years | |||||||
| Developed Technology and Other [Member] | Weighted Average [Member] | ||||||||
| Definite-Lived Intangible Assets [Roll Forward] | ||||||||
| Remaining Useful Life (Years) | 6 years | |||||||
| ||||||||
| X | ||||||||||
- Definition Amount of increase (decrease) in carrying value of assets, excluding financial assets and goodwill, lacking physical substance. No definition available.
|
| X | ||||||||||
- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. No definition available.
|
| X | ||||||||||
- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. No definition available.
|
| X | ||||||||||
- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. No definition available.
|
| X | ||||||||||
- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of increase (decrease) in carrying value of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. No definition available.
|
| X | ||||||||||
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
|
| X | ||||||||||
- Definition Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of increase (decrease) of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
|
| X | ||||||||||
- Definition Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
|||||||||||||
| Investments [Abstract] | ||||||||||||||
| Cash Equivalents | $ 1.5 | $ 3.8 | ||||||||||||
| Recurring Fair Value Measures [Member] | ||||||||||||||
| Investments [Abstract] | ||||||||||||||
| Available-for-sale – Equity Securities | 12.8 | [1] | 10.2 | [2] | ||||||||||
| Available-for-sale – Corporate and Governmental Debt Securities | 8.6 | [1] | 8.9 | [2] | ||||||||||
| Cash Equivalents | 1.5 | [1] | 3.8 | [2] | ||||||||||
| Total Fair Value of Assets | 22.9 | 22.9 | ||||||||||||
| Liabilities [Abstract] | ||||||||||||||
| Deferred Compensation | 20.5 | [3] | 18.2 | [4] | ||||||||||
| U.S. Water Services Contingent Consideration | 5.6 | [5] | 5.4 | [4] | ||||||||||
| Total Fair Value of Liabilities | 26.1 | 23.6 | ||||||||||||
| Total Net Fair Value of Assets (Liabilities) | (3.2) | (0.7) | ||||||||||||
| Activity in Level 3 [Roll Forward] | ||||||||||||||
| Transfers In or Out, All Levels | 0.0 | 0.0 | ||||||||||||
| Recurring Fair Value Measures [Member] | Level 1 [Member] | ||||||||||||||
| Investments [Abstract] | ||||||||||||||
| Available-for-sale – Equity Securities | 12.8 | [1] | 10.2 | [2] | ||||||||||
| Available-for-sale – Corporate and Governmental Debt Securities | 0.0 | [1] | 0.0 | [2] | ||||||||||
| Cash Equivalents | 1.5 | [1] | 3.8 | [2] | ||||||||||
| Total Fair Value of Assets | 14.3 | 14.0 | ||||||||||||
| Liabilities [Abstract] | ||||||||||||||
| Deferred Compensation | 0.0 | [3] | 0.0 | [4] | ||||||||||
| U.S. Water Services Contingent Consideration | 0.0 | [5] | 0.0 | [4] | ||||||||||
| Total Fair Value of Liabilities | 0.0 | 0.0 | ||||||||||||
| Total Net Fair Value of Assets (Liabilities) | 14.3 | 14.0 | ||||||||||||
| Recurring Fair Value Measures [Member] | Level 2 [Member] | ||||||||||||||
| Investments [Abstract] | ||||||||||||||
| Available-for-sale – Equity Securities | 0.0 | [1] | 0.0 | [2] | ||||||||||
| Available-for-sale – Corporate and Governmental Debt Securities | 8.6 | [1] | 8.9 | [2] | ||||||||||
| Cash Equivalents | 0.0 | [1] | 0.0 | [2] | ||||||||||
| Total Fair Value of Assets | 8.6 | 8.9 | ||||||||||||
| Liabilities [Abstract] | ||||||||||||||
| Deferred Compensation | 20.5 | [3] | 18.2 | [4] | ||||||||||
| U.S. Water Services Contingent Consideration | 0.0 | [5] | 0.0 | [4] | ||||||||||
| Total Fair Value of Liabilities | 20.5 | 18.2 | ||||||||||||
| Total Net Fair Value of Assets (Liabilities) | (11.9) | (9.3) | ||||||||||||
| Recurring Fair Value Measures [Member] | Level 3 [Member] | ||||||||||||||
| Investments [Abstract] | ||||||||||||||
| Available-for-sale – Equity Securities | 0.0 | [1] | 0.0 | [2] | ||||||||||
| Available-for-sale – Corporate and Governmental Debt Securities | 0.0 | [1] | 0.0 | [2] | ||||||||||
| Cash Equivalents | 0.0 | [1] | 0.0 | [2] | ||||||||||
| Total Fair Value of Assets | 0.0 | 0.0 | ||||||||||||
| Liabilities [Abstract] | ||||||||||||||
| Deferred Compensation | 0.0 | [3] | 0.0 | [4] | ||||||||||
| U.S. Water Services Contingent Consideration | 5.6 | [5] | 5.4 | [4] | ||||||||||
| Total Fair Value of Liabilities | 5.6 | 5.4 | ||||||||||||
| Total Net Fair Value of Assets (Liabilities) | (5.6) | (5.4) | ||||||||||||
| Activity in Level 3 [Roll Forward] | ||||||||||||||
| Beginning Balance | 5.4 | |||||||||||||
| Ending Balance | 5.6 | $ 5.4 | ||||||||||||
| Recurring Fair Value Measures [Member] | Level 3 [Member] | Accretion [Member] | ||||||||||||||
| Activity in Level 3 [Roll Forward] | ||||||||||||||
| Accretion | $ 0.2 | |||||||||||||
| ||||||||||||||
| X | ||||||||||
- Definition This element represents the portion of the balance sheet assertion, Deferred Compensation, valued at fair value by the entity. No definition available.
|
| X | ||||||||||
- Definition The amount of transfers in and out of levels 1, 2, and 3 of the fair value hierarchy during the period. No definition available.
|
| X | ||||||||||
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (available-for-sale), classified as noncurrent. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Equity securities categorized neither as held-to-maturity nor trading which are intended be sold more than one year from the balance sheet date or operating cycle, if longer. No definition available.
|
| X | ||||||||||
- Definition Amount of liability recognized arising from contingent consideration in a business combination. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
|
| X | ||||||||||
- Definition Amount of increase (decrease) of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Fair value of asset after deduction of liability. No definition available.
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Fair value of financial and nonfinancial obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount of noncurrent assets that are pledged or subject to withdrawal restrictions, classified as other. No definition available.
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|
Fair Value - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Fair Value of Financial Instruments [Line Items] | ||
| Long-Term Debt, Including Long-Term Debt Due Within One Year - Carrying Amount | $ 1,528.8 | $ 1,513.3 |
| Level 2 [Member] | ||
| Fair Value of Financial Instruments [Line Items] | ||
| Long-Term Debt, Including Long-Term Debt Due Within One Year - Fair Value | $ 1,572.8 | $ 1,627.6 |
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. No definition available.
|
| X | ||||||||||
- Details
|
Fair Value - Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | 12 Months Ended |
|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Member] | |||
| Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Abstract] | |||
| Indicators of Impairment | $ 0.0 | $ 0.0 | $ 0.0 |
| X | ||||||||||
- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
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Regulatory Matters - Electric Rates (Details) $ in Millions |
1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
May 25, 2018
USD ($)
|
Apr. 02, 2018
USD ($)
|
Jan. 18, 2018
USD ($)
|
Aug. 09, 2017 |
Apr. 13, 2017
USD ($)
|
Dec. 31, 2016
USD ($)
|
Nov. 30, 2016
USD ($)
|
Jun. 30, 2018
USD ($)
Customers
Years
MW
|
Jun. 30, 2017
USD ($)
|
Jun. 30, 2018
USD ($)
Customers
Years
MW
|
Jun. 30, 2017
USD ($)
|
Dec. 31, 2017
USD ($)
|
|
| Regulatory Matters [Line Items] | ||||||||||||
| Pre-Tax Charge to Fuel, Purchase Power and Gas - Utility | $ 96.5 | $ 93.1 | $ 197.4 | $ 189.7 | ||||||||
| MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Pre-Tax Charge to Fuel, Purchase Power and Gas - Utility | $ 19.5 | |||||||||||
| MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Boswell Energy Center [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Expected Decrease in Annual Depreciation Expense | 25.0 | 25.0 | ||||||||||
| PSCW [Member] | 2016 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Approved Return on Common Equity | 10.50% | |||||||||||
| Approved Equity Ratio | 55.00% | |||||||||||
| Expected Annualized Collection of Additional Revenue Under Retail Rate Order | $ 2.5 | |||||||||||
| PSCW [Member] | 2012 Wisconsin Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Approved Return on Common Equity | 10.90% | |||||||||||
| PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Average Rate Increase | 2.70% | |||||||||||
| Requested Return on Equity | 10.50% | |||||||||||
| Requested Equity Ratio | 55.41% | |||||||||||
| Annual Additional Revenue Generated from Requested Final Rate Increase | $ 2.4 | |||||||||||
| Electric Rates [Member] | MPUC [Member] | Minnesota Cost Recovery Riders [Member] | Minnesota Power [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Revenue from Cost Recovery Riders | 28.0 | 24.4 | $ 52.1 | 48.6 | ||||||||
| Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Average Rate Increase | 9.00% | |||||||||||
| Requested Return on Equity | 10.25% | |||||||||||
| Requested Equity Ratio | 53.81% | |||||||||||
| Annual Additional Revenue Generated from Requested Final Rate Increase | $ 13.0 | $ 55.0 | ||||||||||
| Annual Additional Revenue Generated from Requested Interim Rate Increase | $ 32.2 | $ 34.7 | 49.0 | |||||||||
| Annual Additional Revenue Generated from Requested Final Rate Increase, Amended | $ 49.0 | |||||||||||
| Approved Return on Common Equity | 9.25% | |||||||||||
| Approved Equity Ratio | 53.81% | |||||||||||
| Reserve for Interim Rate Refund | 49.2 | 49.2 | 32.3 | |||||||||
| Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Minimum [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Reconsideration of Certain Decisions Representing Annualized Additional Revenue | $ 20.0 | |||||||||||
| Electric Rates [Member] | MPUC [Member] | 2016 Minnesota General Rate Case [Member] | Minnesota Power [Member] | Retail Customers [Member] | Maximum [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Reconsideration of Certain Decisions Representing Annualized Additional Revenue | $ 25.0 | |||||||||||
| Electric Rates [Member] | MPUC [Member] | Energy-Intensive Trade-Exposed Customer Rates [Member] | Minnesota Power [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Provided Discounts to EITE Customers | 3.8 | $ 3.6 | 8.1 | $ 5.9 | $ 8.6 | |||||||
| Expected Discounts to EITE Customers Annually | $ 15.0 | $ 15.0 | ||||||||||
| Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Number of Customers | Customers | 16 | 16 | ||||||||||
| Length of Notice Required to Terminate (Years) | Years | 3 | 3 | ||||||||||
| Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Termination Effective June 2019) [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Average Monthly Demand (MW) | MW | 29 | 29 | ||||||||||
| Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Number of Customers | Customers | 3 | 3 | ||||||||||
| Electric Rates [Member] | FERC [Member] | FERC-Approved Wholesale Rates [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Wholesale Electric Contracts (Expire from 2024 through 2029) [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Number of Customers | Customers | 14 | 14 | ||||||||||
| Electric Rates [Member] | PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Average Rate Increase | 2.00% | |||||||||||
| Natural Gas [Member] | PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Average Rate Increase | 2.30% | |||||||||||
| Water [Member] | PSCW [Member] | 2018 Wisconsin General Rate Case [Member] | SWL&P [Member] | Retail Customers [Member] | ||||||||||||
| Regulatory Matters [Line Items] | ||||||||||||
| Requested Average Rate Increase | 8.30% | |||||||||||
| X | ||||||||||
- Definition Average demand measured for a specified customer, measured in MW. No definition available.
|
| X | ||||||||||
- Definition Discount Provided to EITE Customers No definition available.
|
| X | ||||||||||
- Definition Estimated Discount to be Provided During the Next Twelve Months No definition available.
|
| X | ||||||||||
- Definition Fuel, Purchased Power and Gas - Utility No definition available.
|
| X | ||||||||||
- Definition Increase (Decrease) in Annual Depreciation Expense Based on Regulatory Order No definition available.
|
| X | ||||||||||
- Definition The length of notice required to terminate a contract (in years). No definition available.
|
| X | ||||||||||
- Definition Number of Customers No definition available.
|
| X | ||||||||||
- Definition Public Utilities, Approved Rate Increase (Decrease), Reconsideration Amount No definition available.
|
| X | ||||||||||
- Definition Reserve for Interim Rate Refund No definition available.
|
| X | ||||||||||
- Definition Percentage of public utility's approved equity to capital, including debt and equity. No definition available.
|
| X | ||||||||||
- Definition Amount of public utility's approved rate increase (decrease) by regulatory agency. No definition available.
|
| X | ||||||||||
- Definition Percentage of public utility's approved return on equity. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency. No definition available.
|
| X | ||||||||||
- Definition Percentage of public utility's requested equity to capital, including debt and equity. No definition available.
|
| X | ||||||||||
- Definition Amount of public utility's amended requested rate increase (decrease) with regulatory agency. No definition available.
|
| X | ||||||||||
- Definition Amount of public utility's requested rate increase (decrease) with regulatory agency. No definition available.
|
| X | ||||||||||
- Definition Percentage of public utility's requested rate increase (decrease) with regulatory agency. No definition available.
|
| X | ||||||||||
- Definition Percentage of public utility's requested return on equity. No definition available.
|
| X | ||||||||||
- Definition The amount of regulated other operating revenues recognized during the period. No definition available.
|
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Regulatory Matters - Integrated Resource Plan (Details) - MPUC [Member] - MW |
Jul. 28, 2017 |
Jun. 18, 2018 |
Dec. 31, 2016 |
|---|---|---|---|
| Minnesota Power [Member] | Resource Package [Member] | Natural Gas PPA [Member] | |||
| Regulatory Matters [Line Items] | |||
| Output Being Purchased (MW) | 250 | ||
| Natural Gas-fired [Member] | Minnesota Power [Member] | Resource Package [Member] | Natural Gas PPA [Member] | |||
| Regulatory Matters [Line Items] | |||
| Expected Output Entitlement (Percent) | 50.00% | ||
| Natural Gas-fired [Member] | Minimum [Member] | Resource Package [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Combined-Cycle Natural Gas-fired Generating Facility [Member] | Jointly Owned Electricity Generation Plant [Member] | |||
| Regulatory Matters [Line Items] | |||
| Generating Capacity to be Jointly Owned (MW) | 525 | ||
| Natural Gas-fired [Member] | Minimum [Member] | Minnesota Power [Member] | Integrated Resource Plan [Member] | |||
| Regulatory Matters [Line Items] | |||
| Additional Natural Gas-fired Generation (MW) | 200 | ||
| Natural Gas-fired [Member] | Maximum [Member] | Resource Package [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Combined-Cycle Natural Gas-fired Generating Facility [Member] | Jointly Owned Electricity Generation Plant [Member] | |||
| Regulatory Matters [Line Items] | |||
| Generating Capacity to be Jointly Owned (MW) | 550 | ||
| Natural Gas-fired [Member] | Maximum [Member] | Minnesota Power [Member] | Integrated Resource Plan [Member] | |||
| Regulatory Matters [Line Items] | |||
| Additional Natural Gas-fired Generation (MW) | 300 | ||
| Wind Turbine Generators [Member] | Minnesota Power [Member] | Resource Package [Member] | Tenaska [Member] | Tenaska PPA [Member] | |||
| Regulatory Matters [Line Items] | |||
| Generating Capacity to be Counterparty Owned (MW) | 250 | ||
| Solar Energy Generation [Member] | Minnesota Power [Member] | Resource Package [Member] | Solar Energy PPA [Member] | |||
| Regulatory Matters [Line Items] | |||
| Generating Capacity to be Counterparty Owned (MW) | 10 | 10 |
| X | ||||||||||
- Definition Generating Capacity Counterparty Owned (MW) No definition available.
|
| X | ||||||||||
- Definition Generating Capacity Jointly Owned (MW) No definition available.
|
| X | ||||||||||
- Definition Capacity of a generating facility, unit, or project in megawatts. No definition available.
|
| X | ||||||||||
- Definition Long-Term Contract for Purchase of Electric Power, Share of Plant Output Purchased No definition available.
|
| X | ||||||||||
- Definition Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
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Regulatory Matters - Great Northern Transmission Line (Details) - Great Northern Transmission Line [Member] $ in Millions |
Jun. 30, 2018
USD ($)
kV
Miles
|
|---|---|
| Regulatory Matters [Line Items] | |
| Transmission Line Length (Miles) | Miles | 220 |
| Transmission Line Capacity (kV) | kV | 500 |
| Total Project Costs Incurred to Date | $ 248.8 |
| Minimum [Member] | |
| Regulatory Matters [Line Items] | |
| Total Project Cost in the U.S. | 560.0 |
| Maximum [Member] | |
| Regulatory Matters [Line Items] | |
| Total Project Cost in the U.S. | 710.0 |
| Minnesota Power [Member] | Minimum [Member] | |
| Regulatory Matters [Line Items] | |
| Total Project Cost in the U.S. | 300.0 |
| Minnesota Power [Member] | Maximum [Member] | |
| Regulatory Matters [Line Items] | |
| Total Project Cost in the U.S. | 350.0 |
| Manitoba Hydro [Member] | |
| Regulatory Matters [Line Items] | |
| Project Costs Recovered from Counterparty | $ 129.2 |
| MPUC [Member] | Minnesota Power [Member] | |
| Regulatory Matters [Line Items] | |
| Transmission Line Length (Miles) | Miles | 220 |
| Transmission Line Capacity (kV) | kV | 500 |
| X | ||||||||||
- Definition Capital cost spent to date for project. No definition available.
|
| X | ||||||||||
- Definition Capital Costs Spent To Date, Recovered No definition available.
|
| X | ||||||||||
- Definition The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period. No definition available.
|
| X | ||||||||||
- Definition Capacity of a transmission line in kilovolts. No definition available.
|
| X | ||||||||||
- Definition Length of a transmission line in miles. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
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Regulatory Matters - Conservation Improvement Program (Details) - MPUC [Member] - USD ($) $ in Millions |
6 Months Ended | ||
|---|---|---|---|
Apr. 02, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
|
| CIP Consolidated Filing [Member] | Minnesota Power [Member] | |||
| Regulatory Matters [Line Items] | |||
| Requested CIP Financial Incentive | $ 3.3 | ||
| Approved Financial Incentive | $ 5.5 | ||
| Minimum [Member] | |||
| Regulatory Matters [Line Items] | |||
| CIP Spending Minimum - Percentage | 1.50% |
| X | ||||||||||
- Definition Minnesota Next Generation Act of 2007 introduced a spend goal of 1.5% of net gross operating revenues from service provided in the state on energy CIPs each year. No definition available.
|
| X | ||||||||||
- Definition Requested CIP Financial Incentive No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition The amount of regulated other operating revenues recognized during the period. No definition available.
|
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Regulatory Matters - MISO Return on Equity Complaints (Details) - FERC [Member] |
Jun. 30, 2018 |
|---|---|
| Regulatory Matters [Line Items] | |
| FERC Authorized Return on Common Equity | 10.32% |
| FERC Authorized Return on Equity Including Incentive Adder | 10.82% |
| Return on Equity Complaint [Member] | |
| Regulatory Matters [Line Items] | |
| Proposed Return on Equity by Federal Administrative Law Judge | 9.70% |
| Proposed Return on Equity by Federal Administrative Law Judge Including Incentive Adder | 10.20% |
| X | ||||||||||
- Definition FERC Authorized Return on Common Equity No definition available.
|
| X | ||||||||||
- Definition FERC Authorized Return on Equity, Including Incentive Adder No definition available.
|
| X | ||||||||||
- Definition The proposed return on common equity by regulatory organization No definition available.
|
| X | ||||||||||
- Definition Proposed Return on Equity by Regulatory Organization, Including Incentive Adder No definition available.
|
| X | ||||||||||
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|
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Regulatory Matters - Minnesota Solar Energy Standard (Details) - MPUC [Member] |
Jun. 30, 2018
MW
|
|---|---|
| Regulatory Matters [Line Items] | |
| Minnesota Solar Energy Standard - Overall Mandate Percentage | 1.50% |
| Minimum [Member] | |
| Regulatory Matters [Line Items] | |
| Minnesota Solar Energy Standard - Overall Mandate Percentage | 1.50% |
| Minnesota Solar Energy Standard - Small Scale Solar Mandate Percentage | 10.00% |
| Maximum [Member] | |
| Regulatory Matters [Line Items] | |
| Minnesota Solar Energy Standard - Qualifying Capacity for Small Scale Solar Mandate (MW) | 0.04 |
| Minnesota Solar Energy Standard [Member] | Minnesota Power [Member] | |
| Regulatory Matters [Line Items] | |
| Minnesota Solar Energy Standard - Percentage of Overall Mandate Expected to be Met with Current Filings or Projects | 33.00% |
| Minnesota Solar Energy Standard - Camp Ripley Project [Member] | Minnesota Power [Member] | |
| Regulatory Matters [Line Items] | |
| Generating Capacity Owned (MW) | 10 |
| Minnesota Solar Energy Standard - Community Solar Garden Project - Purchased Output [Member] | Minnesota Power [Member] | |
| Regulatory Matters [Line Items] | |
| Generating Capacity Counterparty Owned (MW) | 1 |
| Minnesota Solar Energy Standard - Community Solar Garden Project - Owned and Operated [Member] | Minnesota Power [Member] | |
| Regulatory Matters [Line Items] | |
| Generating Capacity Owned (MW) | 0.04 |
| X | ||||||||||
- Definition Generating Capacity Counterparty Owned (MW) No definition available.
|
| X | ||||||||||
- Definition Capacity of a generating facility, unit, or project in megawatts. No definition available.
|
| X | ||||||||||
- Definition Minnesota's solar energy mandate for total retail electric sales, excluding sales to certain industrial customers, by the end of 2020. No definition available.
|
| X | ||||||||||
- Definition The percentage of the solar energy standard overall mandate expected to be met with current filings and projects. No definition available.
|
| X | ||||||||||
- Definition The maximum amount of nameplate capacity of a solar device to qualify for counting towards the small scale solar mandate of Minnesota's solar energy standard. No definition available.
|
| X | ||||||||||
- Definition Minnesota's solar energy mandate for small scale solar with photovoltaic devices with a nameplate capacity of 20 kilowatts or less by the end of 2020. Expressed as a percentage of the overall mandate. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
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Regulatory Matters - Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions |
6 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Regulatory Assets and Liabilities Currently Earning a Return | No regulatory assets or liabilities are currently earning a return. | ||||||||
| Non-Current Regulatory Assets | $ 374.5 | $ 384.7 | |||||||
| Current Regulatory Liabilities | [1] | 39.2 | 0.0 | ||||||
| Non-Current Regulatory Liabilities | 516.0 | 532.0 | |||||||
| Total Regulatory Liabilities | 555.2 | 532.0 | |||||||
| Minnesota Power [Member] | Retail Customers [Member] | Electric Rates [Member] | Energy-Intensive Trade-Exposed Customer Rates [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Provided Discounts to EITE Customers that will be Offset Against Interim Rate Refunds | 16.7 | ||||||||
| Minnesota Power [Member] | Retail Customers [Member] | Electric Rates [Member] | Energy-Intensive Trade-Exposed Customer Rates [Member] | MPUC [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Provided Discounts to EITE Customers that will be Offset Against Interim Rate Refunds | 8.6 | ||||||||
| Provision for Interim Rate Refund [Domain] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Current Regulatory Liabilities | [1],[2] | 32.5 | 0.0 | ||||||
| Provision for Tax Reform Refund [Domain] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Current Regulatory Liabilities | [1],[3] | 6.7 | 0.0 | ||||||
| Income Taxes [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | 401.4 | 411.2 | |||||||
| Wholesale and Retail Contra AFUDC [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | 60.2 | 57.9 | |||||||
| Plant Removal Obligations [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | 23.0 | 20.3 | |||||||
| Cost Recovery Riders [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | 16.8 | 2.2 | |||||||
| North Dakota Investment Tax Credits [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | 14.4 | 14.1 | |||||||
| Provision for Interim Rate Refund [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | [2] | 0.0 | 23.7 | ||||||
| Other | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Liabilities | 0.2 | 2.6 | |||||||
| Defined Benefit Pension and Other Postretirement Benefit Plans [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | 216.7 | 220.3 | |||||||
| Income Taxes [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | 109.3 | 112.8 | |||||||
| Asset Retirement Obligations [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | 31.0 | 29.6 | |||||||
| Manufactured Gas Plant [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | 8.0 | 8.1 | |||||||
| PPACA Income Tax Deferral [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | 5.0 | 5.0 | |||||||
| Conservation Improvement Program [Member] | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | 0.0 | 3.3 | |||||||
| Other | |||||||||
| Regulatory Assets and Liabilities [Line Items] | |||||||||
| Non-Current Regulatory Assets | $ 4.5 | $ 5.6 | |||||||
| |||||||||
| X | ||||||||||
- Definition Provided Discounts to EITE Customers to be Offset Against Interim Rate Refunds No definition available.
|
| X | ||||||||||
- Definition Regulatory Assets and Liabilities [Line Items] No definition available.
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| X | ||||||||||
- 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. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Identifies what net regulatory assets are earning a return through rate billings. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Investment in ATC (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||||
|---|---|---|---|---|---|---|---|
Jul. 31, 2018 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|||
| ALLETE's Investment in ATC [Roll Forward] | |||||||
| Equity Investment Balance as of December 31, 2017 | $ 118.7 | ||||||
| Cash Investments | 3.9 | $ 5.0 | |||||
| Equity in ATC Earnings | $ 4.3 | $ 5.3 | 9.0 | $ 11.4 | |||
| Equity Investment Balance as of June 30, 2018 | $ 123.6 | $ 123.6 | |||||
| FERC [Member] | Return on Equity Complaint [Member] | |||||||
| ALLETE's Investment in ATC [Roll Forward] | |||||||
| Proposed Return on Equity | 9.70% | 9.70% | |||||
| Proposed Return on Equity, Including Incentive Adder | 10.20% | 10.20% | |||||
| ATC [Member] | |||||||
| Investment in ATC [Line Items] | |||||||
| Ownership Percentage | 8.00% | 8.00% | |||||
| Expected Additional Investment in 2018 | $ 1.3 | $ 1.3 | |||||
| ALLETE's Investment in ATC [Roll Forward] | |||||||
| Equity Investment Balance as of December 31, 2017 | 118.7 | ||||||
| Cash Investments | 3.9 | ||||||
| Equity in ATC Earnings | 9.0 | ||||||
| Distributed ATC Earnings | (8.6) | ||||||
| Amortization of the Remeasurement of Deferred Income Taxes | [1] | 0.6 | |||||
| Equity Investment Balance as of June 30, 2018 | $ 123.6 | $ 123.6 | |||||
| Authorized Return on Equity | 10.32% | 10.32% | |||||
| Authorized Return on Equity, Including Incentive Adder | 10.82% | 10.82% | |||||
| ATC [Member] | Subsequent Event [Member] | |||||||
| ALLETE's Investment in ATC [Roll Forward] | |||||||
| Cash Investments | $ 1.2 | ||||||
| |||||||
| X | ||||||||||
- Definition ALLETE's Investment in ATC [Roll Forward] No definition available.
|
| X | ||||||||||
- Definition Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments No definition available.
|
| X | ||||||||||
- Definition The approved percentage return on common equity dedicated to the utility plant in the investee accounted for under the equity method of accounting. No definition available.
|
| X | ||||||||||
- Definition The approved percentage return on common equity, including an incentive adder for participation in a regional transmission organization dedicated to the utility plant in the investee accounted for under the equity method of accounting. No definition available.
|
| X | ||||||||||
- Definition Additional investments expected to be made during the current fiscal year but after the filing date, not already separately disclosed as part of current period/year-to-date investments or as a subsequent event. No definition available.
|
| X | ||||||||||
- Definition The proposed return on common equity, which would be dedicated to the utility plant in the investee accounted for under the equity method of accounting. No definition available.
|
| X | ||||||||||
- Definition The proposed return on common equity, including an incentive adder for participation in a regional transmission organization, which would be dedicated to the utility plant in the investee accounted for under the equity method of accounting. No definition available.
|
| X | ||||||||||
- Definition Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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Short-Term and Long-Term Debt (Details) - USD ($) $ in Millions |
Apr. 16, 2018 |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Debt Instrument [Line Items] | |||
| Short-Term Debt - Principal | $ 57.1 | $ 64.6 | |
| Short-Term Debt - Unamortized Debt Issuance Costs | (0.4) | (0.5) | |
| Short-Term Debt - Total | 56.7 | 64.1 | |
| Long-Term Debt - Principal | 1,471.7 | 1,448.7 | |
| Long-Term Debt - Unamortized Debt Issuance Costs | (9.5) | (9.5) | |
| Long-Term Debt - Total | 1,462.2 | 1,439.2 | |
| Total Debt - Principal | 1,528.8 | 1,513.3 | |
| Total Debt - Unamortized Debt Issuance Costs | (9.9) | (10.0) | |
| Total Debt - Total | $ 1,518.9 | $ 1,503.3 | |
| ALLETE First Mortgage Bonds 4.07% Due April 2048 [Member] | |||
| Debt Instrument [Line Items] | |||
| First Mortgage Bonds - Proceeds from Sale | $ 60.0 | ||
| First Mortgage Bonds - Interest Rate | 4.07% |
| X | ||||||||||
- Definition Amount of short-term debt and current maturities of long-term debt before deduction of unamortized discount or premium and unamortized debt issuance costs. No definition available.
|
| X | ||||||||||
- Definition Represents the aggregate of total long-term debt, including current maturities and short-term debt, before deduction of unamortized discount or premium and unamortized debt issuance expense. No definition available.
|
| X | ||||||||||
- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of short-term debt or the current maturities of long-term debt. No definition available.
|
| X | ||||||||||
- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of long-term debt excluding current maturities. No definition available.
|
| X | ||||||||||
- Definition Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Contractual interest rate for funds borrowed, under the debt agreement. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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| X | ||||||||||
- Definition Represents the aggregate of total long-term debt, including current maturities and short-term debt. No definition available.
|
| X | ||||||||||
- Definition Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The cash inflow from amounts received from a long-term debt instrument secured by a first mortgage deed of trust, containing a pledge of real property. The lender has the highest claim on the property in case of default. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Short-Term and Long-Term Debt - Financial Covenants (Details) |
Jun. 30, 2018 |
|---|---|
| Debt Instrument [Line Items] | |
| Actual Ratio of Indebtedness to Total Capitalization | 0.42 |
| Maximum [Member] | |
| Debt Instrument [Line Items] | |
| Required Ratio of Indebtedness to Total Capitalization | 0.65 |
| X | ||||||||||
- Definition Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. No definition available.
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| X | ||||||||||
- Definition Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. No definition available.
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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Income Tax Expense (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | 12 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
||||||
| Current Income Tax Expense (Benefit) [Abstract] | ||||||||||
| Federal | [1] | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 | |||||
| State | [1] | (0.3) | 0.1 | 0.4 | 0.2 | |||||
| Total Current Income Tax Expense (Benefit) | (0.3) | 0.1 | 0.4 | 0.2 | ||||||
| Deferred Income Tax Expense (Benefit) [Abstract] | ||||||||||
| Federal | [2] | (7.4) | 3.8 | (14.2) | 11.1 | |||||
| State | 2.4 | 3.6 | 5.0 | 9.5 | ||||||
| Investment Tax Credit Amortization | (0.1) | (0.2) | (0.3) | (0.4) | ||||||
| Total Deferred Income Tax Expense (Benefit) | (5.1) | 7.2 | (9.5) | 20.2 | ||||||
| Total Income Tax Expense (Benefit) | (5.4) | 7.3 | (9.1) | 20.4 | ||||||
| Reconciliation of Taxes from Federal Statutory Rate to Total Income Tax Expense [Abstract] | ||||||||||
| Income Before Non-Controlling Interest and Income Taxes | $ 25.9 | $ 44.2 | $ 73.2 | $ 106.3 | ||||||
| Statutory Federal Income Tax Rate | 21.00% | 35.00% | 21.00% | 35.00% | 35.00% | |||||
| Income Taxes Computed at Statutory Federal Rate | $ 5.4 | $ 15.5 | $ 15.4 | $ 37.2 | ||||||
| Increase (Decrease) in Income Tax Due to: [Abstract] | ||||||||||
| State Income Taxes – Net of Federal Income Tax Benefit | 1.6 | 2.4 | 4.2 | 6.3 | ||||||
| Production Tax Credits | (11.2) | (10.0) | (25.6) | (23.0) | ||||||
| Other | (1.2) | (0.6) | (3.1) | (0.1) | ||||||
| Total Income Tax Expense (Benefit) | (5.4) | $ 7.3 | $ (9.1) | $ 20.4 | ||||||
| Effective Tax Rate | 12.40% | 19.20% | ||||||||
| Uncertain Tax Positions [Abstract] | ||||||||||
| Gross Unrecognized Tax Benefits | 1.7 | $ 1.7 | $ 1.7 | |||||||
| Gross Unrecognized Tax Benefits That Would Favorably Impact Effective Income Tax Rate | $ 0.8 | $ 0.8 | ||||||||
| ||||||||||
| X | ||||||||||
- Definition Increase (Decrease) in Tax [Abstract] No definition available.
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| X | ||||||||||
- Definition Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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| X | ||||||||||
- Definition Amount of current state and local tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of deferred federal income tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- References No definition available.
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- Definition Amount of other deferred income tax expense (benefit) pertaining to income (loss) from continuing operations. For example, but not limited to, acquisition-date income tax benefits or expenses recognized from changes in the acquirer's valuation allowance for its previously existing deferred tax assets resulting from a business combination and adjustments to beginning-of-year balance of a valuation allowance because of a change in circumstance causing a change in judgment about the realizability of the related deferred tax asset in future periods. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of deferred state and local tax expense (benefit) pertaining to income (loss) from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority noncontrolling interest income (loss), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, increase (decrease) in enacted tax rate, prior year income taxes, increase (decrease) in deferred tax asset valuation allowance, and other adjustments. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to state and local income tax expense (benefit). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other tax credits. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- References No definition available.
|
| X | ||||||||||
- Definition Amount of unrecognized tax benefits. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
Earnings Per Share and Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Earnings Per Share - Basic [Abstract] | ||||
| Net Income Attributable to ALLETE | $ 31.3 | $ 36.9 | $ 82.3 | $ 85.9 |
| Average Common Shares | 51.3 | 50.9 | 51.2 | 50.5 |
| Earnings Per Share | $ 0.61 | $ 0.73 | $ 1.61 | $ 1.70 |
| Earnings Per Share - Diluted [Abstract] | ||||
| Net Income Attributable to ALLETE | $ 31.3 | $ 36.9 | $ 82.3 | $ 85.9 |
| Average Common Shares | 51.5 | 51.1 | 51.4 | 50.7 |
| Earnings Per Share | $ 0.61 | $ 0.72 | $ 1.60 | $ 1.69 |
| Dilutive Securities (Shares) | 0.2 | 0.2 | 0.2 | 0.2 |
| Common Stock [Member] | ||||
| Class of Stock [Line Items] | ||||
| Options to Purchase Shares Excluded from Computation of Diluted Earnings Per Share | 0.0 | 0.0 | ||
| X | ||||||||||
- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Details
|
Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|||||
| Components of Net Periodic Benefit Cost (Income) [Abstract] | ||||||||
| Employer Contributions to Defined Benefit Pension Plans - Common Stock Value | $ 0.0 | $ 13.5 | ||||||
| Pension [Member] | ||||||||
| Components of Net Periodic Benefit Cost (Income) [Abstract] | ||||||||
| Service Cost | $ 2.8 | $ 2.6 | 5.5 | 5.1 | ||||
| Interest Cost | 7.4 | 8.2 | 14.8 | [1] | 16.3 | [1] | ||
| Expected Return on Plan Assets | (11.1) | (10.6) | (22.1) | [1] | (21.2) | [1] | ||
| Amortization of Prior Service Credits | 0.0 | 0.0 | 0.0 | [1] | 0.0 | [1] | ||
| Amortization of Net Loss | 3.0 | 2.4 | 6.0 | [1] | 4.9 | [1] | ||
| Net Periodic Benefit Cost | 2.1 | 2.6 | 4.2 | 5.1 | ||||
| Employer Contributions to Defined Benefit Pension Plans - Common Stock Value | 13.5 | |||||||
| Employer Contributions to Defined Benefit Plans | 15.0 | 1.7 | ||||||
| Expected Future Employer Contributions in 2018 | 0.0 | 0.0 | ||||||
| Other Postretirement [Member] | ||||||||
| Components of Net Periodic Benefit Cost (Income) [Abstract] | ||||||||
| Service Cost | 1.3 | 1.1 | 2.5 | 2.2 | ||||
| Interest Cost | 1.8 | 1.9 | 3.6 | [1] | 3.8 | [1] | ||
| Expected Return on Plan Assets | (2.8) | (2.7) | (5.5) | [1] | (5.3) | [1] | ||
| Amortization of Prior Service Credits | (0.5) | (0.5) | (0.9) | [1] | (1.0) | [1] | ||
| Amortization of Net Loss | 0.2 | 0.1 | 0.4 | [1] | 0.2 | [1] | ||
| Net Periodic Benefit Cost | 0.0 | $ (0.1) | 0.1 | (0.1) | ||||
| Employer Contributions to Defined Benefit Plans | 0.0 | $ 0.0 | ||||||
| Expected Future Employer Contributions in 2018 | $ 0.0 | $ 0.0 | ||||||
| ||||||||
| X | ||||||||||
- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- Definition Amount of cost recognized for passage of time related to defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan. No definition available.
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| X | ||||||||||
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| X | ||||||||||
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Commitments, Guarantees and Contingencies - Power Purchase Agreements (Details) $ in Millions |
6 Months Ended | |
|---|---|---|
|
Jun. 30, 2018
USD ($)
MW
|
Jun. 30, 2017
USD ($)
|
|
| Square Butte [Member] | Square Butte PPA [Member] | ||
| Power Purchase Agreements [Line Items] | ||
| PPA Counterparty Total Debt Outstanding | $ 311.4 | |
| Cost of Power Purchased | 37.7 | $ 40.7 |
| Pro Rata Share of PPA Counterparty Interest Expense | $ 4.6 | $ 4.7 |
| Square Butte [Member] | Square Butte PPA [Member] | Square Butte Coal-fired Unit [Member] | ||
| Power Purchase Agreements [Line Items] | ||
| Generating Capacity Counterparty Owned (MW) | MW | 455 | |
| Expected Output Entitlement | 50.00% | |
| Minnkota Power [Member] | Square Butte PPA [Member] | Minnkota Power PSA [Member] | Square Butte Coal-fired Unit [Member] | ||
| Power Purchase Agreements [Line Items] | ||
| Expected Output Entitlement | 28.00% | 28.00% |
| Oconto Electric Cooperative [Member] | Oconto Electric Cooperative PSA [Member] | ||
| Power Purchase Agreements [Line Items] | ||
| Energy and Capacity Expected to be Provided (MW) | MW | 25 | |
| X | ||||||||||
- Definition Generating Capacity Counterparty Owned (MW) No definition available.
|
| X | ||||||||||
- Definition Share of plant output being purchased in megawatts under a long-term contract to sell electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. No definition available.
|
| X | ||||||||||
- Definition Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition The allocable portion of interest included in charges under a long-term contract to purchase electric power. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of operating expense for purchased power procured under arrangements extending beyond one year or the normal operating cycle, if longer, by regulated operation. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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| X | ||||||||||
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Commitments, Guarantees and Contingencies - Coal, Rail and Shipping Contracts (Details) - Coal Supply and Transportation Agreements [Member] $ in Millions |
Jun. 30, 2018
USD ($)
|
|---|---|
| Coal, Rail and Shipping Contracts [Line Items] | |
| Minimum Annual Payment Obligation for Remainder of 2018 | $ 16.7 |
| Minimum Annual Payment Obligation in 2019 | 1.7 |
| Minimum Annual Payment Obligation in 2020 | 0.0 |
| Minimum Annual Payment Obligation in 2021 | 0.0 |
| Minimum Annual Payment Obligation in 2022 | 0.0 |
| Minimum Annual Payment Obligation Thereafter | $ 0.0 |
| X | ||||||||||
- Definition Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of the fixed and determinable portion of the unrecorded unconditional purchase obligation maturing in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Details
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Commitments, Guarantees and Contingencies - Leasing Agreements (Details) $ in Millions |
Jun. 30, 2018
USD ($)
|
|---|---|
| Leasing Agreements [Line Items] | |
| Minimum Lease Payments Due for Remainder of 2018 | $ 7.1 |
| Minimum Lease Payments Due in 2019 | 12.8 |
| Minimum Lease Payments Due in 2020 | 9.5 |
| Minimum Lease Payments Due in 2021 | 7.3 |
| Minimum Lease Payments Due in 2022 | 6.1 |
| Minimum Lease Payments Thereafter | 30.0 |
| BNI Energy Dragline [Member] | |
| Leasing Agreements [Line Items] | |
| Minimum Lease Payments Due Annually | 2.8 |
| Termination Fee | 3.0 |
| Minimum Lease Payments Due in 2019 | 2.8 |
| Minimum Lease Payments Due in 2020 | 2.8 |
| Minimum Lease Payments Due in 2021 | 2.8 |
| Minimum Lease Payments Due in 2022 | 2.8 |
| Minimum Lease Payments Thereafter | $ 14.0 |
| X | ||||||||||
- Definition A lump sum payment in conjunction with a lease termination. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
| X | ||||||||||
- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. No definition available.
|
| X | ||||||||||
- Details
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Commitments, Guarantees and Contingencies - Transmission (Details) $ in Millions |
Jun. 30, 2018
USD ($)
kV
Miles
MW
|
|---|---|
| Great Northern Transmission Line [Member] | |
| Transmission [Line Items] | |
| Transmission Line Length (Miles) | Miles | 220 |
| Transmission Line Capacity (kV) | kV | 500 |
| Total Project Costs Incurred to Date | $ 248.8 |
| Great Northern Transmission Line [Member] | Minimum [Member] | |
| Transmission [Line Items] | |
| Total Project Cost in the U.S. | 560.0 |
| Great Northern Transmission Line [Member] | Maximum [Member] | |
| Transmission [Line Items] | |
| Total Project Cost in the U.S. | 710.0 |
| Manitoba Hydro [Member] | Great Northern Transmission Line [Member] | |
| Transmission [Line Items] | |
| Project Costs Recovered from Counterparty | 129.2 |
| Minnesota Power [Member] | Great Northern Transmission Line [Member] | Minimum [Member] | |
| Transmission [Line Items] | |
| Total Project Cost in the U.S. | 300.0 |
| Minnesota Power [Member] | Great Northern Transmission Line [Member] | Maximum [Member] | |
| Transmission [Line Items] | |
| Total Project Cost in the U.S. | $ 350.0 |
| Manitoba Hydro PPA [Member] | Manitoba Hydro [Member] | |
| Transmission [Line Items] | |
| Output Being Purchased (MW) | MW | 250 |
| X | ||||||||||
- Definition Capital cost spent to date for project. No definition available.
|
| X | ||||||||||
- Definition Capital Costs Spent To Date, Recovered No definition available.
|
| X | ||||||||||
- Definition The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period. No definition available.
|
| X | ||||||||||
- Definition Share of plant output being purchased in megawatts under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. No definition available.
|
| X | ||||||||||
- Definition Capacity of a transmission line in kilovolts. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Length of a transmission line in miles. No definition available.
|
| X | ||||||||||
- Details
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| X | ||||||||||
- Details
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Commitments, Guarantees and Contingencies - Environmental Matters (Details) $ in Millions |
6 Months Ended | 12 Months Ended |
|---|---|---|
|
Jun. 30, 2018
USD ($)
MW
|
Dec. 31, 2017
USD ($)
|
|
| Environmental Restoration Costs [Member] | ||
| Environmental Matters [Line Items] | ||
| Estimated Costs of Compliance (Accrued) | $ 7.0 | $ 8.0 |
| NOV Consent Decree [Member] | ||
| Environmental Matters [Line Items] | ||
| Consent Decree Wind Energy Generation Addition (MW) | MW | 200 | |
| Ozone NAAQS [Member] | ||
| Environmental Matters [Line Items] | ||
| Estimated Costs of Compliance | $ 0.0 | |
| NO2 NAAQS [Member] | ||
| Environmental Matters [Line Items] | ||
| Estimated Costs of Compliance | 0.0 | |
| Clean Water Act - Aquatic Organisms [Member] | Maximum [Member] | ||
| Environmental Matters [Line Items] | ||
| Estimated Costs of Compliance | 15.0 | |
| Coal Combustion Residuals [Member] | Minimum [Member] | ||
| Environmental Matters [Line Items] | ||
| Estimated Costs of Compliance | 65.0 | |
| Coal Combustion Residuals [Member] | Maximum [Member] | ||
| Environmental Matters [Line Items] | ||
| Estimated Costs of Compliance | $ 100.0 |
| X | ||||||||||
- Definition [Line Items] for Environmental Matters [Table] No definition available.
|
| X | ||||||||||
- Definition Capacity of a generating facility, unit, or project in megawatts. No definition available.
|
| X | ||||||||||
- Definition Amount of loss exposure accrued and the best estimate of reasonably possible loss exposure in excess of the accrual. No definition available.
|
| X | ||||||||||
- Definition Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
|
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Commitments, Guarantees and Contingencies - Other Matters (Details) - USD ($) $ in Millions |
6 Months Ended | |
|---|---|---|
Jun. 30, 2018 |
Dec. 31, 2017 |
|
| ALLETE Clean Energy [Member] | Letters of Credit [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Collateral | $ 16.2 | |
| U.S. Water Services [Member] | Letters of Credit [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Collateral | 0.0 | |
| BNI Energy Reclamation Liability [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Estimated Obligation | 47.5 | |
| BNI Energy Reclamation Liability [Member] | Letters of Credit [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Collateral | 0.6 | |
| BNI Energy Reclamation Liability [Member] | Surety Bonds [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Collateral | 49.9 | |
| ALLETE Properties Development and Maintenance Obligations [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Estimated Obligation | 6.1 | |
| ALLETE Properties Development and Maintenance Obligations [Member] | Surety Bonds and Letters of Credit [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Collateral | $ 8.6 | |
| Town Center District Capital Improvement Bonds [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Ownership Percentage of Benefited Property | 70.00% | 70.00% |
| Annual Assessment | $ 1.4 | |
| Palm Coast Park District Special Assessment Bonds [Member] | ||
| Guarantor Obligations [Line Items] | ||
| Ownership Percentage of Benefited Property | 27.00% | 33.00% |
| Annual Assessment | $ 0.6 |
| X | ||||||||||
- Definition Amount of annual assessments based on ownership percentage of benefited property related to real estate development projects funded by municipal capital improvement revenue and special assessment bonds. No definition available.
|
| X | ||||||||||
- Definition Ownership percentage of property benefitied by a real estate development project funded by municipal capital improvement revenue and special assessment bonds. No definition available.
|
| X | ||||||||||
- Definition Amount of any assets held either as collateral or by third parties that, upon the occurence of any triggering event or condition under the guarantee, can be obtained and liquidated to recover all or a portion of the amounts paid under the guarantee. No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Commitments, Guarantees and Contingencies - Legal Proceedings (Details) - U.S. Water Services [Member] - U.S. Water Services Patent Defense Litigation [Member] $ in Millions |
6 Months Ended |
|---|---|
|
Jun. 30, 2018
USD ($)
| |
| Legal Proceedings [Line Items] | |
| Patents Infringed | 2 |
| Addition to Intangible Assets for Patent Defense Costs | $ 2 |
| X | ||||||||||
- Definition Finite-Lived Intangible Assets Addition for Patent Defense Costs No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Number of entity's patents that another entity has allegedly infringed. No definition available.
|
| X | ||||||||||
- Details
|
| X | ||||||||||
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|
Business Segments (Details) $ in Millions |
3 Months Ended | 6 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Jun. 30, 2018
USD ($)
a
|
Jun. 30, 2017
USD ($)
|
Jun. 30, 2018
USD ($)
a
Segments
|
Jun. 30, 2017
USD ($)
|
Dec. 31, 2017
USD ($)
|
||||||
| Business Segments [Line Items] | ||||||||||
| Number of Reportable Segments | Segments | 3 | |||||||||
| Operating Revenue | $ 344.1 | $ 353.3 | $ 702.3 | $ 718.9 | ||||||
| Net Income (Loss) | 31.3 | 36.9 | 82.3 | 85.9 | ||||||
| Assets | 5,114.7 | $ 5,114.7 | $ 5,080.0 | |||||||
| Regulated Operations [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Number of Operating Segments | Segments | 3 | |||||||||
| Operating Revenue | 257.8 | 264.9 | $ 528.0 | 546.5 | ||||||
| Net Income (Loss) | 26.0 | 32.4 | 69.9 | 75.9 | ||||||
| Assets | 3,898.2 | 3,898.2 | 3,886.6 | |||||||
| Regulated Operations [Member] | Residential [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 30.7 | 27.6 | 71.4 | 67.1 | |||||
| Regulated Operations [Member] | Commercial [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 36.2 | 33.7 | 72.8 | 71.9 | |||||
| Regulated Operations [Member] | Municipal [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 13.7 | 12.3 | 27.7 | 30.5 | |||||
| Regulated Operations [Member] | Industrial [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 115.3 | 121.6 | 230.2 | 243.3 | |||||
| Regulated Operations [Member] | Other Power Suppliers [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 42.7 | 41.7 | 86.4 | 82.9 | |||||
| Regulated Operations [Member] | Conservation Improvement Programs [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1],[2] | 0.0 | 5.5 | 0.0 | 5.5 | |||||
| Regulated Operations [Member] | Other [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 19.2 | 22.5 | 39.5 | 45.3 | |||||
| ALLETE Clean Energy [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | 18.3 | 19.6 | 42.9 | 43.3 | ||||||
| Net Income (Loss) | 6.8 | 3.8 | 14.9 | 10.5 | ||||||
| Assets | 620.2 | 620.2 | 600.5 | |||||||
| ALLETE Clean Energy [Member] | Long-term PSA [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 12.4 | 13.7 | 31.0 | 31.5 | |||||
| ALLETE Clean Energy [Member] | Other [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue, Other Than Customer Revenue | [1] | 5.9 | 5.9 | 11.9 | 11.8 | |||||
| U.S. Water Services [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | 41.5 | 38.4 | 79.7 | 70.5 | ||||||
| Net Income (Loss) | 0.2 | 0.6 | (1.2) | 0.3 | ||||||
| Assets | 291.8 | 291.8 | 292.4 | |||||||
| U.S. Water Services [Member] | Point-in-Time [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 25.7 | 23.9 | 48.0 | 45.7 | |||||
| U.S. Water Services [Member] | Contract [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 9.5 | 8.8 | 19.0 | 17.7 | |||||
| U.S. Water Services [Member] | Capital Project [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | $ 6.3 | 5.7 | $ 12.7 | 7.1 | |||||
| Corporate and Other [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Number of Operating Segments | Segments | 2 | |||||||||
| Land in Minnesota (Acres) | a | 4,000 | 4,000 | ||||||||
| Operating Revenue | $ 26.5 | 30.4 | $ 51.7 | 58.6 | ||||||
| Net Income (Loss) | (1.7) | 0.1 | (1.3) | (0.8) | ||||||
| Assets | 304.5 | 304.5 | $ 300.5 | |||||||
| Corporate and Other [Member] | Long-term Contract [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | 22.7 | 23.2 | 42.7 | 45.3 | |||||
| Corporate and Other [Member] | Other [Member] | ||||||||||
| Business Segments [Line Items] | ||||||||||
| Operating Revenue | [1] | $ 3.8 | $ 7.2 | $ 9.0 | $ 13.3 | |||||
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- Definition Non-cash Revenue Recognized From Amortization of PSAs Assumed Through Acquisitions No definition available.
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- Definition Area of land held. No definition available.
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- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. No definition available.
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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. No definition available.
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- Definition Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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