Acquisitions (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended			3 Months Ended
	Feb. 11, 2014	Jan. 30, 2014		Mar. 31, 2014		Dec. 31, 2013
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Jan. 30, 2014
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		$ 26.9
Assets [Abstract]
Cash and Cash Equivalents		3.8
Other Current Assets		12.4
Property, Plant and Equipment - Net		161.2
Other Non-Current Assets		8.1	[1]
Total Assets Acquired		185.5
Liabilities [Abstract]
Other Current Liabilities		15.2	[2]
Long-term Debt Due Within One Year		2.2
Long-term Debt		21.1
Power Purchase Agreement		99.4		96.4	[3]	0	[3]
Other Non-Current Liabilities		10.1
Non-Controlling Interest		10.6	[4]
Total Liabilities and Non-Controlling Interest Assumed		158.6
Net Identifiable Assets Acquired		26.9
Power Purchase Agreement		12.4		13.1	[3]	0	[3]
Business Combination, Acquisition Related Costs				1.4
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	6.0
Armenia Mountain [Member]
Business Acquisition [Line Items]
Business Acquisition, Name of Acquired Entity				Armenia Mountain
Generating Capacity (MW)				101
Liabilities [Abstract]
Purchase option		0.3
Goodwill		$ 1.9
Storm Lake [Member]
Business Acquisition [Line Items]
Business Acquisition, Name of Acquired Entity				Storm Lake
Generating Capacity (MW)				77
Condon [Member]
Business Acquisition [Line Items]
Business Acquisition, Name of Acquired Entity				Condon
Generating Capacity (MW)				50
Lake Benton [Member]
Business Acquisition [Line Items]
Business Acquisition, Name of Acquired Entity				Lake Benton
Generating Capacity (MW)				104

[1] Included in Other Non-Current Assets was the fair value estimate of $0.3 million for the option to purchase Armenia Mountain in 2015, and preliminary goodwill of $1.9 million; for tax purposes, the purchase price allocation resulted in no allocation to goodwill.

[2] Other Current Liabilities included $12.4 million related to the current liabilities portion of the Power Purchase Agreements.

[3] Power Purchase Agreements were acquired in conjunction with the ALLETE Clean Energy wind energy facilities acquisition on January 30, 2014 (see Note 4. Acquisitions).

[4] The preliminary purchase price accounting valued the non-controlling interest of Lake Benton, Storm Lake and Condon at fair value primarily on the discounted cash flow method. The non-controlling interest related to Lake Benton and Storm lake was subsequently purchased by ALLETE Clean Energy.