Regulatory Matters - Minnesota Solar Energy Standard (Details) - Dec. 31, 2020 - MPUC [Member] $ in Millions	MW	Total	kW	USD ($)
Regulatory Matters [Line Items]
Minnesota Solar Energy Standard - Overall Mandate Percentage		1.50%
ALLETE, Inc. [Member]
Regulatory Matters [Line Items]
Estimated Investment Amount | $				$ 40
Estimated Generation from Projects Under Development	20
Minnesota Solar Energy Standard - Camp Ripley Project [Member] | Minnesota Power [Member]
Regulatory Matters [Line Items]
Energy Generation Owned (MW)	10		40
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]
Energy Generation Owned (MW)	0.04
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