Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2020

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
2020
Operating Revenue	$311.6	$243.2	$293.9	$320.4
Operating Income	$60.2	$12.7	$41.6	$36.4
Net Income Attributable to ALLETE	$66.3	$20.1	$40.7	$47.1
Earnings Per Share of Common Stock
Basic	$1.28	$0.39	$0.78	$0.91
Diluted	$1.28	$0.39	$0.78	$0.90
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