Document and Entity Information Document - USD ($)
12 Months Ended
Dec. 31, 2016
Feb. 01, 2017
Jun. 30, 2016
Document and Entity Information [Line Items]      
Entity Registrant Name ALLETE INC    
Entity Central Index Key 0000066756    
Entity Tax Identification Number 410418150    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 3,178,250,707
Entity Common Stock, Shares Outstanding   50,049,020  
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY    
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2016