Acquisitions - U.S. Water Services (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended		3 Months Ended
	Feb. 10, 2015		Mar. 31, 2015		Dec. 31, 2014
Liabilities [Abstract]
Restricted Cash			$ 5.6	[1]	$ 2.7	[1]
U.S. Water Services [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition			Feb. 10, 2015
Business Acquisition, Name of Acquired Entity			U.S. Water Services
Business Acquisition, Consideration Transferred	202.3
Payments to Acquire Businesses, Gross	166.6
Business Acquisition, Percentage of Voting Interests Acquired	87.00%
Business Acquisition, Contingent Consideration, Liability	35.7
Business Acquisition, Percent of Results of Operations Reflected in Income Statement			100.00%
Business Acquisition, Effective Percentage of Business Acquired	100.00%
Assets [Abstract]
Cash and Cash Equivalents	0.9
Accounts Receivable	16.8
Inventories	13.4	[2]
Other Current Assets	5.3	[3]
Property, Plant and Equipment	10.6
Goodwill	127.1	[4]
Intangible Assets	83.0	[5]
Other Non-Current Assets	0.2
Total Assets Acquired	257.3
Liabilities [Abstract]
Other Current Liabilities	18.7
Other Non-Current Liabilities	36.3
Total Liabilities and Non-Controlling Interest Assumed	55.0
Net Identifiable Assets Acquired	202.3
Fair Value Adjustments for Work in Process and Finished Goods	2.7
Fair Value of Sales Backlog	1.6
Restricted Cash	2.1
Business Acquisition, Goodwill, Expected Tax Deductible Amount	3.2
Business Acquisition, Acquisition Related Costs			$ 3.0

[1] Restricted Cash related to ALLETE Clean Energy’s wind energy facilities operating expense and capital distribution reserve requirements and cash pledged as collateral by U.S. Water Services for stand-by letters of credit.

[2] Included in Inventories was $2.7 million of fair value adjustments relating to work in process and finished goods inventories which will be recognized as Cost of Sales within one year from the acquisition date.

[3] Included in Other Current Assets was $1.6 million relating to the fair value of sales backlog. Sales backlog will be recognized as Cost of Sales within one year from the acquisition date. Also included in Other Current Assets was restricted cash of $2.1 million relating to cash pledged as collateral for stand-by letters of credit.

[4] Goodwill is largely attributable to strategic opportunities for growing U.S. Water Services and the benefits of the existing workforce. Goodwill of $3.2 million is deductible for tax purposes.

[5] Intangible Assets include customer relationships, patents, non-compete agreements and trademarks and trade names. (See Note 5. Goodwill and Intangible Assets.)