Commitments and Contingencies (Details-1) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) Tons ppb MW
Columbia Environmental Project, SCR [Member] | MGE [Member]
Columbia Commitments
Share of projected project cost, minimum | $	$ 19
Share of projected project cost, maximum | $	$ 29
EPA [Member] | Legal Entity Type of Counterparty [Domain]
Effluent Limitations Guidelines and Standards for Steam Electric Power Generating Source Category [Abstract]
Air pollution control and ash handling systems capacity at coal burning power plants, minimum (in MW) | MW	50
EPA's Greenhouse Gas Reduction Guidelines
National average reduction of greenhouse gas emissions by the year 2030, percentage	32.00%
Compliance plan preparation term related to the greenhouse gas emissions reduction guidelines	3 years
Sulfur Dioxide NAAQS
Annual maximum level of sulfur dioxide for large stationary sources | Tons	2,000
Ozone NAAQS
Current primary regulated level of Ozone NAAQS (in parts per billion)	70
Current secondary regulated level of Ozone NAAQS (in parts per billion)	70