Document and Entity Information Document	6 Months Ended
	Jun. 30, 2021 shares
Document and Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	1-3548
Entity Registrant Name	ALLETE, Inc.
State of Incorporation	MN
Entity Tax Identification Number	41-0418150
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
Title of 12(b) Security	Common Stock, without par value
Trading Symbol	ALE
Name of Exchange	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	52,268,119
Entity Central Index Key	0000066756
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Small Business	false
Entity Emerging Growth Company	false