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Regulatory Matters - Great Northern Transmission Line (GNTL) (Details) - Great Northern Transmission Line [Member]
Mar. 31, 2016
kV
Miles
Regulatory Matters [Line Items]  
Transmission Line Length (Miles) | Miles 220
Transmission Line Capacity (kV) | kV 500
MPUC [Member] | Great Northern Transmission Line Route Permit [Member] | Minnesota Power [Member]  
Regulatory Matters [Line Items]  
Transmission Line Length (Miles) | Miles 220
Transmission Line Capacity (kV) | kV 500