Earnings Per Share and Common Stock (Tables)

3 Months Ended

Mar. 31, 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
Three Months Ended March 31,
Net Income Attributable to ALLETE		$66.3			$66.3		$70.5			$70.5
Average Common Shares	51.7		0.1	51.8		51.6		0.1	51.7
Earnings Per Share		$1.28			$1.28		$1.37			$1.37