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Regulated Operations - Minnesota Solar Energy Standard (Details)
$ in Millions
Sep. 30, 2020
USD ($)
MW
Regulated Operations [Abstract]  
Estimated Generation from Projects Under Development | MW 20
MPUC [Member] | ALLETE, Inc. [Member]  
Regulated Operations [Abstract]  
Estimated Investment Amount $ 40
Regulatory Matters [Line Items]  
Estimated Investment Amount $ 40