Consolidated Balance Sheet Parentheticals - USD ($)
shares in Millions, $ in Millions
Dec. 31, 2019
Dec. 31, 2018
Accounts Receivable [Abstract]    
Accounts Receivable, Allowance for Credit Loss, Current [1] $ 0.9 $ 1.7
Common Stock [Abstract]    
Common Stock, Par Value Per Share $ 0.00 $ 0.00
Common Stock, Shares Authorized 80.0 80.0
Common Stock, Shares Outstanding 51.7 51.5
Common Stock, Shares Issued 51.7 51.5
[1]
On March 26, 2019, ALLETE sold U.S. Water Services which resulted in the removal of the related accounts receivable from the Consolidated Balance Sheet.