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Regional Transmission Organizations	12 Months Ended
Regional Transmission Organizations	Dec. 31, 2014
Regional Transmission Organizations Disclosure [Abstract]
Regional Transmission Organizations	Regional Transmission Organizations - MGE Energy and MGE. MGE reports on a net basis transactions on the MISO and PJM markets in which it buys and sells power within the same hour to meet electric energy delivery requirements. This treatment resulted in a $91.1 million and $78.0 million reduction to sales to the market and purchase power expense for MISO markets for the years ended December 31, 2014 and 2013, respectively, and a $75.9 million reduction to sales to the market and purchased power expense for MISO and PJM markets for the year ended December 31, 2012.