Consolidated Balance Sheet - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Current Assets [Abstract]
Cash and Cash Equivalents		$ 97.0	$ 97.0
Accounts Receivable (Less Allowance of $1.2 and $1.0)		124.8	121.2
Inventories		116.0	117.1
Prepayments and Other		41.5	35.7
Total Current Assets		379.3	371.0
Property, Plant and Equipment – Net		3,642.3	3,669.1
Regulatory Assets		367.1	372.0
Investment in ATC		128.6	124.5
Other Investments		72.9	74.6
Goodwill and Intangible Assets – Net		213.9	215.2
Other Non-Current Assets		68.6	68.1
Total Assets	[1]	4,872.7	4,894.5
Current Liabilities [Abstract]
Accounts Payable		58.8	88.8
Accrued Taxes		52.2	44.0
Accrued Interest		14.9	18.6
Long-Term Debt Due Within One Year		14.8	35.7
Notes Payable		0.7	1.6
Other		82.8	86.1
Total Current Liabilities		224.2	274.8
Long-Term Debt		1,551.3	1,556.7
Deferred Income Taxes		589.7	579.8
Regulatory Liabilities		102.2	105.0
Defined Benefit Pension and Other Postretirement Benefit Plans		205.7	206.8
Other Non-Current Liabilities		347.1	349.0
Total Liabilities		$ 3,020.2	$ 3,072.1
Commitments, Guarantees and Contingencies (Note 13)
Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 49.3 and 49.1 Shares Outstanding		$ 1,281.0	$ 1,271.4
Accumulated Other Comprehensive Loss		(24.7)	(24.5)
Retained Earnings		593.5	573.3
Total ALLETE Equity		1,849.8	1,820.2
Non-Controlling Interest in Subsidiaries		2.7	2.2
Total Equity		1,852.5	1,822.4
Total Liabilities and Equity		$ 4,872.7	$ 4,894.5

[1] As a result of revised accounting guidance adopted in the first quarter of 2016, we reclassified unamortized debt issuance costs from Other Non-Current Assets to Long-Term Debt on the Consolidated Balance Sheet. Prior period segment assets have been revised to conform to the current presentation. (See Note 1. Operations and Significant Accounting Policies.)