Rate Matters	9 Months Ended
Sep. 30, 2019
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. Lower fuel costs and increase in rate base from renewable generation assets are additional items impacting the rate change. 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. MGE did not file a base rate case for 2018. 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 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%. In July 2019, the PSCW issued a final decision in the 2018 fuel rules proceedings for MGE to refund $9.5 million of additional fuel savings realized during 2018 plus accrued interest to its retail electric customers in October 2019. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred in the previous year. As of September 30, 2019, MGE had deferred $0.5 million in 2019 fuel savings. As of December 31, 2018, MGE had deferred $9.5 million of 2018 fuel savings. c.2018 Tax Reform. Customer rates approved for 2018 reflected an income tax rate of 35 percent. In January 2018, the PSCW issued an order directing Wisconsin investor-owned utilities to defer the over-collection of income tax expense as a result of the decrease in tax rate to 21 percent. The PSCW issued an order in May 2018 to return to customers the estimated 2018 over-collection of income tax expense. The decision included a one-time bill credit on customer bills to reflect the estimate of the over-collection for January through June 2018, along with a volumetric bill credit which began in July 2018 and continued through the remainder of 2018 for the estimated remaining annual amount. MGE returned $8.2 million to customers through bill credits as of December 31, 2018. In August 2019, the PSCW issued a decision on the 2018 tax reform proceedings for MGE to refund the remaining 2018 overcollection of income tax expense to its retail customers as a one-time bill credit. MGE returned $3.2 million in September 2019. There was no change to the refund order from the amount MGE deferred as of December 31, 2018.

Rate Matters

9 Months Ended

Sep. 30, 2019

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. Lower fuel costs and increase in rate base from renewable generation assets are additional items impacting the rate change. 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.

MGE did not file a base rate case for 2018.

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 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%.

In July 2019, the PSCW issued a final decision in the 2018 fuel rules proceedings for MGE to refund $9.5 million of additional fuel savings realized during 2018 plus accrued interest to its retail electric customers in October 2019. There was no change to the refund in the fuel rules proceedings from the amount MGE deferred in the previous year.

As of September 30, 2019, MGE had deferred $0.5 million in 2019 fuel savings. As of December 31, 2018, MGE had deferred $9.5 million of 2018 fuel savings.

c.2018 Tax Reform.

Customer rates approved for 2018 reflected an income tax rate of 35 percent. In January 2018, the PSCW issued an order directing Wisconsin investor-owned utilities to defer the over-collection of income tax expense as a result of the decrease in tax rate to 21 percent.

The PSCW issued an order in May 2018 to return to customers the estimated 2018 over-collection of income tax expense. The decision included a one-time bill credit on customer bills to reflect the estimate of the over-collection for January through June 2018, along with a volumetric bill credit which began in July 2018 and continued through the remainder of 2018 for the estimated remaining annual amount. MGE returned $8.2 million to customers through bill credits as of December 31, 2018.

In August 2019, the PSCW issued a decision on the 2018 tax reform proceedings for MGE to refund the remaining 2018 overcollection of income tax expense to its retail customers as a one-time bill credit. MGE returned $3.2 million in September 2019. There was no change to the refund order from the amount MGE deferred as of December 31, 2018.