Commitments and Contingencies	3 Months Ended
Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies. a. Environmental - MGE Energy and MGE. MGE Energy and MGE are subject to frequently changing local, state, and federal regulations concerning air quality, water quality, land use, threatened and endangered species, hazardous materials handling, and solid waste disposal. These regulations affect the manner in which they conduct their operations, the costs of those operations, as well as capital and operating expenditures. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Regulatory initiatives, proposed rules, and court challenges to adopted rules have the potential to have a material effect on capital expenditures and operating costs. Management believes compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. These initiatives, proposed rules, and court challenges include: • The EPA's published water effluent limitations guidelines and standards for steam electric power plants, which focus on the reduction of metals and other pollutants in wastewater from new and existing power plants, such as the coal-burning plants at Columbia and the Elm Road Units. The operators of the Columbia and the Elm Road Units have indicated that equipment upgrades may be necessary to comply with the new discharge standards. Management believes that any compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. • The EPA's cooling water intake rules, which require cooling water intake structures at electric power plants, such as our Blount and Columbia plants, to meet best available technology standards so that mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens) are reduced. MGE expects that the Section 316(b) rule will not have a material effect on its existing plants. • Greenhouse Gas (GHG) reduction guidelines and approval criteria established under the Clean Air Act for states to use in developing plans to control GHG emissions from existing fossil fuel-fired electric generating units (EGUs). In 2015, the EPA finalized the Clean Power Plan (CPP) which directed states to submit plans, to reduce GHG emissions from the electric generation sector. In February 2016, the U.S. Supreme Court stayed implementation of the CPP and the stay remains in effect. In October 2017, the EPA issued a proposed rule to repeal the CPP. In August 2018, the EPA proposed the Affordable Clean Energy (ACE) rule which would replace the CPP, if successfully implemented. The ACE proposal directs states to submit plans to the EPA for approval that implement standards of performance (called Best System of Emissions Reductions, or BSER) for individual EGUs over 25 MW. ACE defines BSER as on-site, heat-rate efficiency improvements, whereas the CPP defines BSERs using carbon dioxide emission performance rates. Simple cycle units such as our smaller combustion units, and combined cycle units such as our WCCF are exempt from the proposed ACE rule. Under the proposed ACE rule, if a state fails to prepare a plan, or its plan is not approved by the EPA a federal implementation plan will be issued for that state. The proposed ACE rule as it is currently written has the potential to impact Blount, Columbia, and the Elm Road Units. Given the pending legal proceedings, and the proposed ACE rule, the nature and timing of any final requirements is subject to uncertainty. MGE is unable to determine with any certainty the impact of the proposed ACE rule on our operations. If an ACE rule is implemented substantially in the form of the CPP rule, it is expected to have a material impact on MGE. MGE will continue to monitor developments with the proposed ACE rule, and the CPP rule, and related litigation. • The EPA's rule to regulate ambient levels of ozone through the 2015 Ozone National Ambient Air Quality Standards (NAAQS). In May 2018, the EPA issued a final rule which designated the northeast portion of Milwaukee County as being in nonattainment with this NAAQS. The Elm Road Units are located in Milwaukee County, outside the designated nonattainment area. In August 2018, several environmental groups, the City of Chicago, and the State of Illinois filed federal lawsuits challenging several of the EPA's attainment designation decisions, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. MGE is monitoring the outcome of this lawsuit and how it may affect our Elm Road Units in Milwaukee County. At this time, MGE expects that the 2015 Ozone NAAQS will not have a material effect on its existing plants based on final designations. • Rules regulating nitrogen oxide (NO_x) and sulfur dioxide (SO₂) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule (CAVR). MGE has met our CSAPR obligations in 2018 and 2017 through a combination of reduced emissions through pollution control (e.g. SCR installation at Columbia), as well as owned, received, and purchased allowances. There remains uncertainty around CSAPR due to legal challenges, however, MGE expects that we will meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor developments and litigation to this rule. Columbia is subject to the best available retrofit technology (BART) regulations, a subsection of the EPA's CAVR, which may require pollution control retrofits. Columbia's existing pollution control upgrades, and the EPA's stance that compliance with the CSAPR equals compliance with BART, should mean that Columbia will not need to do additional work to meet BART requirements. At this time, however, the BART regulatory obligations, compliance strategies, and costs remain uncertain in Wisconsin due to the continued legal challenges surrounding CSAPR and CAVR. MGE will continue to monitor developments to this rule. • The EPA's Coal Combustion Residuals Rule (CCR), which regulates coal ash from burning coal for the purpose of generating electricity as a solid waste, and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates landfills, ash ponds, and other surface impoundments used for coal combustion residuals by regulating their design, location, monitoring, and operation. Review of the Elm Road Units has indicated that the costs to comply with this rule are not expected to be significant. Columbia's operator has completed a review of their system and has determined that an onsite ash pond will need to be closed and replaced with a dry ash handling system. The dry ash handling system installation is planned for 2020-2021. In July 2018, the EPA published a final rule that included amendments to the CCR (which include the allowance of alternative performance standards for landfills and surface impoundments, revised risk-based groundwater protection standards, and an extension of the deadline by which certain facilities must cease the placement of waste in CCR units). In August 2018, the Court of Appeals for the D.C. Circuit vacated parts of the CCR for not being sufficiently protective of the environment. It is unclear how the EPA will respond to that decision. MGE will continue to monitor potential rule modifications to assess potential impacts on operations. b. Legal Matters - MGE Energy and MGE. MGE is involved in various legal matters that are being defended and handled in the normal course of business. MGE maintains accruals for such costs that are probable of being incurred and subject to reasonable estimation. The accrued amount for these matters is not material to the financial statements. MGE does not expect the resolution of these matters to have a material adverse effect on its consolidated results of operations, financial condition, or cash flows.

Commitments and Contingencies.

a. Environmental - MGE Energy and MGE.

MGE Energy and MGE are subject to frequently changing local, state, and federal regulations concerning air quality, water quality, land use, threatened and endangered species, hazardous materials handling, and solid waste disposal. These regulations affect the manner in which they conduct their operations, the costs of those operations, as well as capital and operating expenditures. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Regulatory initiatives, proposed rules, and court challenges to adopted rules have the potential to have a material effect on capital expenditures and operating costs. Management believes compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects. These initiatives, proposed rules, and court challenges include:

• The EPA's published water effluent limitations guidelines and standards for steam electric power plants, which focus on the reduction of metals and other pollutants in wastewater from new and existing power plants, such as the coal-burning plants at Columbia and the Elm Road Units. The operators of the Columbia and the Elm Road Units have indicated that equipment upgrades may be necessary to comply with the new discharge standards. Management believes that any compliance costs will be recovered in future rates based on previous treatment of environmental compliance projects.

• The EPA's cooling water intake rules, which require cooling water intake structures at electric power plants, such as our Blount and Columbia plants, to meet best available technology standards so that mortality from entrainment (drawing aquatic life into a plant's cooling system) and impingement (trapping aquatic life on screens) are reduced. MGE expects that the Section 316(b) rule will not have a material effect on its existing plants.

• Greenhouse Gas (GHG) reduction guidelines and approval criteria established under the Clean Air Act for states to use in developing plans to control GHG emissions from existing fossil fuel-fired electric generating units (EGUs). In 2015, the EPA finalized the Clean Power Plan (CPP) which directed states to submit plans, to reduce GHG emissions from the electric generation sector. In February 2016, the U.S. Supreme Court stayed implementation of the CPP and the stay remains in effect. In October 2017, the EPA issued a proposed rule to repeal the CPP. In August 2018, the EPA proposed the Affordable Clean Energy (ACE) rule which would replace the CPP, if successfully implemented. The ACE proposal directs states to submit plans to the EPA for approval that implement standards of performance (called Best System of Emissions Reductions, or BSER) for individual EGUs over 25 MW. ACE defines BSER as on-site, heat-rate efficiency improvements, whereas the CPP defines BSERs using carbon dioxide emission performance rates. Simple cycle units such as our smaller combustion units, and combined cycle units such as our WCCF are exempt from the proposed ACE rule. Under the proposed ACE rule, if a state fails to prepare a plan, or its plan is not approved by the EPA a federal implementation plan will be issued for that state. The proposed ACE rule as it is currently written has the potential to impact Blount, Columbia, and the Elm Road Units.

Given the pending legal proceedings, and the proposed ACE rule, the nature and timing of any final requirements is subject to uncertainty. MGE is unable to determine with any certainty the impact of the proposed ACE rule on our operations. If an ACE rule is implemented substantially in the form of the CPP rule, it is expected to have a material impact on MGE. MGE will continue to monitor developments with the proposed ACE rule, and the CPP rule, and related litigation.

• The EPA's rule to regulate ambient levels of ozone through the 2015 Ozone National Ambient Air Quality Standards (NAAQS). In May 2018, the EPA issued a final rule which designated the northeast portion of Milwaukee County as being in nonattainment with this NAAQS. The Elm Road Units are located in Milwaukee County, outside the designated nonattainment area. In August 2018, several environmental groups, the City of Chicago, and the State of Illinois filed federal lawsuits challenging several of the EPA's attainment designation decisions, including the partial Milwaukee County designation as being too narrow and not sufficiently protective. MGE is monitoring the outcome of this lawsuit and how it may affect our Elm Road Units in Milwaukee County. At this time, MGE expects that the 2015 Ozone NAAQS will not have a material effect on its existing plants based on final designations.

• Rules regulating nitrogen oxide (NO_x) and sulfur dioxide (SO₂) emissions, including the Cross State Air Pollution Rule (CSAPR) and Clean Air Visibility Rule (CAVR).

MGE has met our CSAPR obligations in 2018 and 2017 through a combination of reduced emissions through pollution control (e.g. SCR installation at Columbia), as well as owned, received, and purchased allowances. There remains uncertainty around CSAPR due to legal challenges, however, MGE expects that we will meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor developments and litigation to this rule.

Columbia is subject to the best available retrofit technology (BART) regulations, a subsection of the EPA's CAVR, which may require pollution control retrofits. Columbia's existing pollution control upgrades, and the EPA's stance that compliance with the CSAPR equals compliance with BART, should mean that Columbia will not need to do additional work to meet BART requirements. At this time, however, the BART regulatory obligations, compliance strategies, and costs remain uncertain in Wisconsin due to the continued legal challenges surrounding CSAPR and CAVR. MGE will continue to monitor developments to this rule.

• The EPA's Coal Combustion Residuals Rule (CCR), which regulates coal ash from burning coal for the purpose of generating electricity as a solid waste, and defines what ash use activities would be considered generally exempt beneficial reuse of coal ash. The CCR rule also regulates landfills, ash ponds, and other surface impoundments used for coal combustion residuals by regulating their design, location, monitoring, and operation.

Review of the Elm Road Units has indicated that the costs to comply with this rule are not expected to be significant. Columbia's operator has completed a review of their system and has determined that an onsite ash pond will need to be closed and replaced with a dry ash handling system. The dry ash handling system installation is planned for 2020-2021.

In July 2018, the EPA published a final rule that included amendments to the CCR (which include the allowance of alternative performance standards for landfills and surface impoundments, revised risk-based groundwater protection standards, and an extension of the deadline by which certain facilities must cease the placement of waste in CCR units). In August 2018, the Court of Appeals for the D.C. Circuit vacated parts of the CCR for not being sufficiently protective of the environment. It is unclear how the EPA will respond to that decision. MGE will continue to monitor potential rule modifications to assess potential impacts on operations.