Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Investments [Abstract]
ALLETE Properties	$ 88,200,000		$ 89,900,000
Available-for-sale Securities	18,900,000	[1]	17,700,000	[1]	26,800,000
Cash Equivalents	2,900,000	[2]	34,200,000	[2]
Other	4,400,000		4,500,000
Total Other Investments	114,400,000		146,300,000
Available-for-sale Corporate Debt Securities, Maturities, One Year or Less	600,000
Available-for-sale Corporate Debt Securities, Maturities, One Year to Less Than Three Years	1,700,000
Available-for-sale Corporate Debt Securities, Maturities, Three Years to Less Than Five Years	2,600,000
Available-for-sale Corporate Debt Securities, Maturities, Five or More Years	5,900,000
ALLETE Properties [Roll Forward]
Land Inventory Beginning Balance	83,800,000		85,400,000		86,500,000
Cost of Sales	(2,200,000)		(1,500,000)
Other	600,000		400,000
Land Inventory Ending Balance	83,800,000		85,400,000		86,500,000
Long-Term Finance Receivables (net of allowances of $0.6 and $0.6)	1,200,000		1,400,000
Other	3,200,000		3,100,000
Total Real Estate Assets	88,200,000		89,900,000
Land Impairment	0		0		0
Long-Term Finance Receivables, Allowance	$ 600,000		$ 600,000

[1] As of December 31, 2014, the aggregate amount of available-for-sale corporate debt securities maturing in one year or less was $0.6 million, in one year to less than three years was $1.7 million, in three years to less than five years was $2.6 million, and in five or more years was $5.9 million.

[2] During 2014, cash included in Other Investments was transferred to Cash and Cash Equivalents.