Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2019

Selected Quarterly Financial Information [Abstract]

Quarterly Financial Data (Unaudited) [Table Text Block]

Quarter Ended	Mar. 31		Jun. 30		Sept. 30		Dec. 31
Millions Except Earnings Per Share
2019
Operating Revenue		$357.2		$290.4		$288.3		$304.6
Operating Income		$56.8		$36.2		$37.0		$49.8
Net Income Attributable to ALLETE		$70.5		$34.2		$31.2		$49.7
Earnings Per Share of Common Stock
Basic		$1.37		$0.66		$0.60		$0.96
Diluted		$1.37		$0.66		$0.60		$0.96
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