Short-Term and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Apr. 02, 2013	Mar. 31, 2013	Dec. 31, 2012
Financial Covenants [Abstract]
Required Indebtedness to Total Capital Ratio		0.65
Actual Indebtedness to Total Capital Ratio		0.45
Debt Instrument [Line Items]
Short-Term Debt Outstanding		$ 41.2	$ 84.5
Long-Term Debt Outstanding		975.1	933.6
Proceeds from Issuance of First Mortgage Bonds	150.0
ALLETE Bonds 4.86% Series Due 2013 [Member]
Debt Instrument [Line Items]
Long-Term Debt Outstanding		60.0
ALLETE Bonds 1.83% Due April 2018 [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of First Mortgage Bonds	50.0
First Mortgage Bonds, Interest Rate	1.83%
ALLETE Bonds 3.30% Due October 2028 [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of First Mortgage Bonds	40.0
First Mortgage Bonds, Interest Rate	3.30%
ALLETE Bonds 4.21% Due October 2043 [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of First Mortgage Bonds	$ 60.0
First Mortgage Bonds, Interest Rate	4.21%