Consolidated Balance Sheet - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Current Assets [Abstract]
Cash and Cash Equivalents	$ 60.6	$ 145.8
Accounts Receivable (Less Allowance of $1.1 and $1.1)	103.9	103.0
Inventories	107.8	80.5
Prepayments and Other	36.5	82.0
Deferred Income Taxes	21.8	7.5
Total Current Assets	330.6	418.8
Property, Plant and Equipment – Net	3,451.5	3,284.8
Regulatory Assets	359.6	357.3
Investment in ATC	124.2	121.1
Other Investments	115.0	114.4
Goodwill and Intangible Assets – Net	213.4	4.8
Other Non-Current Assets	78.7	59.6
Total Assets	4,673.0	4,360.8
Current Liabilities [Abstract]
Accounts Payable	94.8	134.1
Accrued Taxes	34.9	38.7
Accrued Interest	17.7	18.0
Long-Term Debt Due Within One Year	118.0	100.7
Notes Payable	0.0	3.7
Other	135.6	120.8
Total Current Liabilities	401.0	416.0
Long-Term Debt	1,272.4	1,272.8
Deferred Income Taxes	572.5	510.7
Regulatory Liabilities	104.8	94.2
Defined Benefit Pension and Other Postretirement Benefit Plans	190.0	190.9
Other Non-Current Liabilities	353.9	265.0
Total Liabilities	$ 2,894.6	$ 2,749.6
Commitments, Guarantees and Contingencies (Note 16)
Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 48.9 and 45.9 Shares Outstanding	$ 1,257.1	$ 1,107.6
Unearned ESOP Shares	(3.3)	(7.2)
Accumulated Other Comprehensive Loss	(20.2)	(21.1)
Retained Earnings	543.0	530.1
Total ALLETE Equity	1,776.6	1,609.4
Non-Controlling Interest in Subsidiaries	1.8	1.8
Total Equity	1,778.4	1,611.2
Total Liabilities and Equity	$ 4,673.0	$ 4,360.8