Short-Term and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended
	Mar. 04, 2014	Dec. 10, 2013	Mar. 31, 2014	Jan. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Short-Term Debt Outstanding			$ 11.1		$ 27.2
Short-Term Debt Outstanding, Subsequently Matured			11.1		27.2
Long-Term Debt Outstanding			1,202.5		1,083.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt				23.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt				2.2
Expected Proceeds from Future Issuance of First Mortgage Bonds		215.0
Proceeds from Issuance of First Mortgage Bonds	100.0
ALLETE Bonds 4.86% Series Due 2013 [Member]
Debt Instrument [Line Items]
Short-Term Debt Outstanding, Subsequently Matured					18.0
ALLETE Bonds 3.69% Due March2024 [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of First Mortgage Bonds	60.0
Debt Instrument, Interest Rate, Stated Percentage	3.69%
ALLETE Bonds 4.95% Due March2044 [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of First Mortgage Bonds	40.0
Debt Instrument, Interest Rate, Stated Percentage	4.95%
ALLETE Bonds 3.40% Due July2022 [Member]
Debt Instrument [Line Items]
Expected Proceeds from Future Issuance of First Mortgage Bonds		75.0
Future Debt Instrument, Interest Rate, Stated Percentage		3.40%
ALLETE Bonds 5.05% Due July2044 [Member]
Debt Instrument [Line Items]
Expected Proceeds from Future Issuance of First Mortgage Bonds		$ 40.0
Future Debt Instrument, Interest Rate, Stated Percentage		5.05%