XML 84 R70.htm IDEA: XBRL DOCUMENT v3.8.0.1
Business Segments (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
a
Sep. 30, 2016
USD ($)
Sep. 30, 2017
USD ($)
a
Segments
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Business Segments [Line Items]          
Number of Reportable Segments | Segments     3    
Operating Revenue $ 362.5 $ 349.6 $ 1,081.4 $ 998.2  
Net Income (Loss) Attributable to ALLETE 44.9 40.3 130.8 111.0  
Assets 4,978.5   $ 4,978.5   $ 4,876.9
Regulated Operations [Member]          
Business Segments [Line Items]          
Number of Operating Segments | Segments     3    
Operating Revenue 277.6 253.3 $ 824.1 740.5  
Net Income (Loss) Attributable to ALLETE 34.2 45.0 110.1 110.0  
Assets 3,811.7   3,811.7   3,823.9
ALLETE Clean Energy [Member]          
Business Segments [Line Items]          
Operating Revenue 13.5 14.7 56.8 57.1  
Net Income (Loss) Attributable to ALLETE 0.6 1.0 11.1 9.7  
Assets 560.3   560.3   566.0
U.S. Water Services [Member]          
Business Segments [Line Items]          
Operating Revenue 40.2 37.8 110.7 104.5  
Net Income (Loss) Attributable to ALLETE 1.3 1.5 1.6 2.0  
Assets $ 293.3   $ 293.3   264.1
Corporate and Other [Member]          
Business Segments [Line Items]          
Number of Operating Segments | Segments     2    
Land in Minnesota (Acres) | a 5,000   5,000    
Operating Revenue $ 31.2 43.8 $ 89.8 96.1  
Net Income (Loss) Attributable to ALLETE 8.8 $ (7.2) 8.0 $ (10.7)  
Assets $ 313.2   $ 313.2   $ 222.9