Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Information [Abstract]

Quarterly Financial Data (Unaudited) [Text Block]

QUARTERLY FINANCIAL DATA (UNAUDITED)

Information for any one quarterly period is not necessarily indicative of the results which may be expected for the year.

Quarter Ended	Mar. 31		Jun. 30		Sept. 30		Dec. 31
Millions Except Earnings Per Share
2018
Operating Revenue		$358.2		$344.1		$348.0		$448.3
Operating Income		$57.4		$36.5		$43.3		$64.0
Net Income Attributable to ALLETE		$51.0		$31.3		$30.7		$61.1
Earnings Per Share of Common Stock
Basic		$1.00		$0.61		$0.59		$1.19
Diluted		$0.99		$0.61		$0.59		$1.18
2017
Operating Revenue		$365.6		$353.3		$362.5		$337.9
Operating Income		$71.6		$54.0		$68.0		$32.3
Net Income Attributable to ALLETE		$49.0		$36.9		$44.9		$41.4
Earnings Per Share of Common Stock
Basic		$0.97		$0.73		$0.88		$0.81
Diluted		$0.97		$0.72		$0.88		$0.81
2016
Operating Revenue		$333.8		$314.8		$349.6		$341.5
Operating Income		$65.2		$40.6		$51.8		$59.4
Net Income Attributable to ALLETE		$45.9		$24.8		$40.3		$44.3
Earnings Per Share of Common Stock
Basic		$0.93		$0.50		$0.82		$0.89
Diluted		$0.93		$0.50		$0.81		$0.89