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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

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Generating Capacity Jointly Owned (MW)

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- 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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.D)
-URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030

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