Earnings Per Share and Common Stock (Tables)

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

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

			2017					2016
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		$44.9			$44.9		$40.3			$40.3
Average Common Shares	51.0		0.2	51.2		49.4		0.1	49.5
Earnings Per Share		$0.88			$0.88		$0.82			$0.81
Nine Months Ended September 30,
Net Income Attributable to ALLETE		$130.8			$130.8		$111.0			$111.0
Average Common Shares	50.7		0.2	50.9		49.3		0.1	49.4
Earnings Per Share		$2.58			$2.57		$2.25			$2.25