Rate Matters	12 Months Ended
Rate Matters	Dec. 31, 2018
Regulated Operations [Abstract]
Rate Matters	Rate Matters - MGE Energy and MGE. a. Rate Proceedings. In December 2018, the PSCW approved the settlement agreement between MGE and intervening parties in the rate case. The settlement decreases electric rates by 2.24% or $9.2 million in 2019. MGE will maintain this rate level for 2020, with the exception that MGE will file a 2020 Fuel Cost Plan in 2019 and MGE's electric rates will be adjusted accordingly. The decrease reflects the ongoing tax impacts of the Tax Act and the addition of lower-cost renewable generation capacity. The settlement agreement increases gas rates by 1.06% or $1.7 million in 2019 and 1.46% or $2.4 million in 2020. The gas increase covers infrastructure costs. It also reflects the impacts of the Tax Act. The return on common stock equity for 2019 and 2020 is 9.8% based on a capital structure consisting of 56.6% common equity in 2019 and 56.1% common equity in 2020. In December 2016, the PSCW authorized MGE, effective January 1, 2017, to decrease 2017 rates for retail electric customers by 0.8% or $3.3 million on an annual basis and to increase rates for retail gas customers by 1.9% or $3.1 million on an annual basis. The decrease in retail electric rates was attributable to declining fuel and purchased power costs. The increase in retail gas rates covered costs associated with MGE's natural gas system infrastructure improvements. The authorized return on common stock equity for 2017 was 9.8% based on a capital structure consisting of 57.2% common equity. MGE did not file a base rate case for 2018 and 2016. b. Fuel Rules. Fuel rules require the PSCW and Wisconsin utilities to defer electric fuel-related costs that fall outside a symmetrical cost tolerance band around the amount approved for a utility in its annual fuel proceedings. Any over/under recovery of the actual costs is determined in the following year and is then reflected in future billings to electric retail customers. The fuel rules bandwidth is currently set at plus or minus 2%. Under fuel rules, MGE would defer costs, less any excess revenues, if its actual electric fuel costs exceeded 102% of the electric fuel costs allowed in its latest rate order. Excess revenues are defined as revenues in the year in question that provide MGE with a greater return on common equity than authorized by the PSCW in MGE's latest rate order. Conversely, MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than 98% of the electric fuel costs allowed in that order. These costs will be subject to the PSCW's annual review of fuel costs completed in the year following the deferral. In August 2015, the PSCW approved a $0.00256/kWh fuel credit that began on September 1, 2015, and continued throughout 2016. MGE returned $8.3 million of electric fuel-related savings during the year ended December 31, 2017. The PSCW issued final decisions in the fuel rules proceedings for MGE to refund additional fuel savings incurred to its retail electric customers over a one-month period. MGE returned $4.2 million, $6.2 million, and $15.5 million of electric fuel-related savings in October 2018, October 2017, and September 2016, respectively. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred in the previous respective years. In December 2017, the PSCW approved a surcharge for 2018 electric fuel-related costs. The surcharge increased electric retail revenue in 2018 by $0.5 million or 0.13%. As of December 31, 2018, MGE has deferred $9.5 million of 2018 fuel-related savings. These costs will be subject to the PSCW's annual review of 2018 fuel costs, expected to be completed in 2019.