Earnings Per Share and Common Stock (Tables)

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

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

		2020			2019
Reconciliation of Basic and Diluted		Dilutive			Dilutive
Earnings Per Share	Basic	Securities	Diluted	Basic	Securities	Diluted
Millions Except Per Share Amounts
Quarter ended September 30,
Net Income Attributable to ALLETE	$40.7		$40.7	$31.2		$31.2
Average Common Shares	51.9	0.1	52.0	51.7	0.1	51.8
Earnings Per Share	$0.78		$0.78	$0.60		$0.60
Nine Months Ended September 30,
Net Income Attributable to ALLETE	$127.1		$127.1	$135.9		$135.9
Average Common Shares	51.8	0.1	51.9	51.6	0.1	51.7
Earnings Per Share	$2.45		$2.45	$2.63		$2.63