| Cover | Nov. 30, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 30, 2020 |
| Entity Registrant Name | ALLETE, Inc |
| Entity Incorporation, State or Country Code | MN |
| Entity File Number | 1-3548 |
| Entity Tax Identification Number | 41-0418150 |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock, without par value |
| Trading Symbol | ALE |
| Security Exchange Name | NYSE |
| Entity Address, Address Line One | 30 West Superior Street |
| Entity Address, City or Town | Duluth |
| Entity Address, State or Province | MN |
| Entity Address, Postal Zip Code | 55802-2093 |
| City Area Code | 218 |
| Local Phone Number | 279-5000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Central Index Key | 0000066756 |
| Amendment Flag | false |
