Regulatory Matters - Integrated Resource Plan (Details) - MPUC [Member] - Resource Package [Member]	Jul. 28, 2017 MW
Natural Gas-fired [Member] | Combined-Cycle Natural Gas-Fired Generating Facility [Member] | Minimum [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Jointly Owned Electricity Generation Plant [Member]
Regulatory Matters [Line Items]
Generating Capacity to be Jointly Owned (MW)	525
Natural Gas-fired [Member] | Combined-Cycle Natural Gas-Fired Generating Facility [Member] | Maximum [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Jointly Owned Electricity Generation Plant [Member]
Regulatory Matters [Line Items]
Generating Capacity to be Jointly Owned (MW)	550
Minnesota Power [Member] | Natural Gas PPA [Member]
Regulatory Matters [Line Items]
Output Being Purchased (MW)	250
Minnesota Power [Member] | Natural Gas-fired [Member] | Natural Gas PPA [Member]
Regulatory Matters [Line Items]
Expected Output Entitlement (Percent)	50.00%
Minnesota Power [Member] | Wind Turbine Generators [Member] | Nobles 2 [Member] | Nobles 2 [Member]
Regulatory Matters [Line Items]
Generating Capacity to be Counterparty Owned (MW)	250
Minnesota Power [Member] | Solar Energy Generation [Member] | Solar Energy PPA [Member]
Regulatory Matters [Line Items]
Generating Capacity to be Counterparty Owned (MW)	10