Consolidated Statement of Shareholders' Equity - USD ($) $ in Millions	Total	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Unearned ESOP Shares [Member]	Common Stock [Member]
Beginning Balance at Dec. 31, 2012	$ 1,201.0	$ 459.6	$ (22.0)	$ (21.3)	$ 784.7
Comprehensive Income
Net Income	104.7	104.7
Other Comprehensive Income – Net of Tax
Unrealized Loss on Securities – Net	0.0
Unrealized Gain on Derivatives – Net	0.1		0.1
Defined Benefit Pension and Other Postretirement Plans – Net	4.8		4.8
Total Comprehensive Income	109.6
Non-Controlling Interest in Subsidiaries	0.0
Comprehensive Income Attributable to ALLETE	109.6
Common Stock Issued – Net	100.5				100.5
Dividends Declared	(75.2)	(75.2)
ESOP Shares Earned	7.0			7.0
Ending Balance at Dec. 31, 2013	1,342.9	489.1	(17.1)	(14.3)	885.2
Comprehensive Income
Net Income	125.5	125.5
Other Comprehensive Income – Net of Tax
Unrealized Loss on Securities – Net	(0.2)		(0.2)
Unrealized Gain on Derivatives – Net	0.2		0.2
Defined Benefit Pension and Other Postretirement Plans – Net	(4.0)		(4.0)
Total Comprehensive Income	121.5
Non-Controlling Interest in Subsidiaries	(0.7)	(0.7)
Comprehensive Income Attributable to ALLETE	120.8
Common Stock Issued – Net	222.4				222.4
Dividends Declared	(83.8)	(83.8)
ESOP Shares Earned	7.1			7.1
Ending Balance at Dec. 31, 2014	1,609.4	530.1	(21.1)	(7.2)	1,107.6
Comprehensive Income
Net Income	141.5	141.5
Other Comprehensive Income – Net of Tax
Unrealized Loss on Securities – Net	(0.5)		(0.5)
Unrealized Gain on Derivatives – Net	0.1		0.1
Defined Benefit Pension and Other Postretirement Plans – Net	(3.0)		(3.0)
Total Comprehensive Income	138.1
Non-Controlling Interest in Subsidiaries	(0.4)	(0.4)
Comprehensive Income Attributable to ALLETE	137.7
Common Stock Issued – Net	163.8				163.8
Dividends Declared	(97.9)	(97.9)
ESOP Shares Earned	7.2			7.2
Ending Balance at Dec. 31, 2015	$ 1,820.2	$ 573.3	$ (24.5)	$ 0.0	$ 1,271.4