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Pension and Other Postretirement Benefit Plans - Contributions (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified | 12 Months Ended | 3 Months Ended | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Mar. 31, 2014 Pension [Member] | Dec. 31, 2014 Pension [Member] | Dec. 31, 2013 Pension [Member] | Dec. 31, 2012 Pension [Member] | Dec. 31, 2014 Postretirement Health and Life [Member] | Dec. 31, 2013 VEBA [Member] | Dec. 31, 2012 VEBA [Member] | Dec. 31, 2013 Grantor Trust [Member] | Dec. 31, 2012 Grantor Trust [Member]
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plans, Employer Contributions |  |  |  |  |  | $ 0 | $ 7.3 |  | $ 10.8 | $ 1.5 | $ 2.0 | $ 0
ALLETE Common Stock Contributed to Pension Plan | 0 | 0 | 20.0 | 19.5 |  |  |  |  |  |  |  |
ALLETE Common Stock Contributed to Pension Plan, Shares |  |  |  | 400 |  |  |  |  |  |  |  |
Defined Benefit Plans, Estimated Employer Contributions |  |  |  |  | We do not expect to make any additional contributions to the defined benefit pension plan in 2014, beyond the $19.5 million contribution to the defined benefit pension plan made in January 2014. |  |  |  |  |  |  |
Defined Benefit Plans, Estimated Employer Contributions |  |  |  |  |  |  |  | 0 |  |  |  |
Defined Contribution Plan, Employer Contributions | $ 8.4 | $ 7.7 |  |  |  |  |  |  |  |  |  |

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- Definition Amount employer contributed during the period, to match employee contributions, to a defined contribution plan. Includes, but not limited to, contributions made through Employee Stock Ownership Plans (ESOP). + References No definition available. + Details
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- Definition Descriptive information regarding the employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions. Description may include a range of expected contributions, required minimum contribution, whether the expected contribution is discretionary, and further explanation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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- Definition Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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- Definition The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its pension plans and its non-pension postretirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585 + Details
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- Definition Number of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan. + References No definition available. + Details
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- Definition Value of shares issued during the period to an employee benefit plan, such as a defined contribution or defined benefit plan. + References No definition available. + Details
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