Commitments and Contingencies (Details-3) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Tons ppb pollutant phase state MW
Columbia Environmental Project, SCR [Member] | MGE [Member]
Columbia
Share of projected SCR project cost, minimum | $	$ 19
Share of projected SCR project cost, maximum | $	$ 29
Wisconsin Energy Efficiency and Renewables Act [Member]
Energy Efficiency and Renewables
Minimum electricity generated from renewable resources by 2015	10.00%
EPA [Member]
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
EPA's National Ambient Air Quality Standards
Number of pollutants monitored by the National Ambient Air Quality Standards | pollutant	6
EPA's Ozone NAAQS
Current primary regulated level of Ozone NAAQS (in parts per billion) | ppb	70
Current secondary regulated level of Ozone NAAQS (in parts per billion) | ppb	70
EPA's Sulfur Dioxide NAAQS
Annual maximum level of sulfur dioxide for large stationary sources | Tons	2,000
Number of phases for for attainment and nonattainment area designation | phase	3
EPA's Cross State Air Pollution Rule
Number of eastern states identified contributing to pollution in other states | state	27
Number of phases for allocation of NOx and SO2 allowances to qualifying power plants under the rule | phase	2
Number of states incorporating 2008 ozone NAAQS attainment levels | state	23