Common Stock and Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Summary of Common Stock [Table Text Block]

Summary of Common Stock	Shares	Equity
	Thousands	Millions
Balance as of December 31, 2019	51,679	$1,436.7
Employee Stock Purchase Plan	13	0.7
Invest Direct	309	18.3
Share-Based Compensation	84	5.2
Balance as of December 31, 2020	52,085	1,460.9
Employee Stock Purchase Plan	17	0.8
Invest Direct	263	17.5
Share-Based Compensation	73	6.5
Equity Issuance Program	782	51.0
Balance as of December 31, 2021	53,220	1,536.7
Employee Stock Purchase Plan	11	0.9
Invest Direct	244	14.9
Share-Based Compensation	82	5.3
Equity Issuance	3,680	223.7
Balance as of December 31, 2022	57,237	$1,781.5

Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block]

Reconciliation of Basic and Diluted
Earnings Per Share		Dilutive
Year Ended December 31	Basic	Securities	Diluted
Millions Except Per Share Amounts
2022
Net Income Attributable to ALLETE	$189.3		$189.3
Average Common Shares	55.9	0.1	56.0
Earnings Per Share	$3.38		$3.38
2021
Net Income Attributable to ALLETE	$169.2		$169.2
Average Common Shares	52.4	0.1	52.5
Earnings Per Share	$3.23		$3.23
2020
Net Income Attributable to ALLETE	$165.4		$165.4
Average Common Shares	51.9	—	51.9
Earnings Per Share	$3.18		$3.18