Consilidated Statement of Income (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Statement of Income [Abstract]
Operating Revenue	$ 1,136.8	$ 1,018.4	$ 961.2
Operating Expenses
Fuel and Purchased Power	356.1	334.8	308.7
Operating and Maintenance	456.2	412.9	397.1
Depreciation	135.7	116.6	100.2
Total Operating Expenses	948.0	864.3	806.0
Operating Income	188.8	154.1	155.2
Other Income (Expense)
Interest Expense	(54.8)	(50.3)	(45.5)
Equity Earnings in ATC	19.6	20.3	19.4
Other	8.6	9.3	6.0
Total Other Expense	(26.6)	(20.7)	(20.1)
Income Before Non-Controlling Interest and Income Taxes	162.2	133.4	135.1
Income Tax Expense	36.7	28.7	38.0
Net Income	125.5	104.7	97.1
Less: Non-Controlling Interest in Subsidiaries	0.7	0	0
Net Income Attributable to ALLETE	$ 124.8	$ 104.7	$ 97.1
Average Shares of Common Stock and Per Share Data
Basic (in shares)	42.9	39.7	37.6
Diluted (in shares)	43.1	39.8	37.6
Basic Earnings Per Share of Common Stock	$ 2.91	$ 2.64	$ 2.59
Diluted Earnings Per Share of Common Stock	$ 2.90	$ 2.63	$ 2.58
Dividends Per Share of Common Stock	$ 1.96	$ 1.90	$ 1.84