Consolidated Balance Sheet (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Current Assets [Abstract]
Cash and Cash Equivalents	$ 135.1	$ 44.9
Short-Term Investments	0	6.7
Accounts Receivable (Less Allowance of $0.9 and $0.9)	75.8	99.5
Inventories	69.1	60.0
Prepayments and Other	22.8	28.6
Total Current Assets	302.8	239.7
Property, Plant and Equipment - Net	1,902.1	1,805.6
Regulatory Assets	286.9	310.2
Investment in ATC	97.9	93.3
Other Investments	129.5	126.0
Other Non-Current Assets	35.2	34.3
Total Assets	2,754.4	2,609.1
Current Liabilities [Abstract]
Accounts Payable	44.1	75.4
Accrued Taxes	20.3	22.0
Accrued Interest	13.0	13.4
Long-Term Debt Due Within One Year	12.8	13.4
Notes Payable	5.6	1.0
Other	26.2	33.7
Total Current Liabilities	122.0	158.9
Long-Term Debt	844.4	771.6
Deferred Income Taxes	373.0	325.2
Regulatory Liabilities	44.6	43.6
Defined Benefit Pension and Other Postretirement Benefit Plans	217.1	231.4
Other Non-Current Liabilities	101.9	93.4
Total Liabilities	1,703.0	1,624.1
Commitments and Contingencies (Note 14)
ALLETE's Equity [Abstract]
Common Stock Without Par Value, 80 Shares Authorized, 36.8 and 35.8 Shares Outstanding	676.7	636.1
Unearned ESOP Shares	(30.3)	(36.8)
Accumulated Other Comprehensive Loss	(22.7)	(23.2)
Retained Earnings	427.7	399.9
Total ALLETE Equity	1,051.4	976.0
Non-Controlling Interest in Subsidiaries	0	9.0
Total Equity	1,051.4	985.0
Total Liabilities and Equity	$ 2,754.4	$ 2,609.1