Commitments and Contingencies	3 Months Ended
Mar. 31, 2020
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 operations are conducted, the costs of 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 could 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. MGE is currently evaluating proposed rule modifications for applicability to the Columbia and Elm Road Units. Until the modifications are finalized, MGE will not know with certainty how operations will be impacted. •The EPA's cooling water intake rules, which require cooling water intake structures at electric power plants to meet best available technology (BAT) 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 will need to conduct studies at its Blount plant by the end of 2021 to determine BAT. Columbia's operators will also need to determine BAT. Future BAT requirements at Blount and Columbia will be based on the results of these intake studies and will be specified in the next permits expected to be issued in 2023 or later. MGE expects that this 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 2019, the EPA published a final rule creating the Affordable Clean Energy (ACE) rule to reduce greenhouse gas emissions from existing coal-fired EGUs. The ACE rule 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 coal-fired EGUs over 25 MW. The ACE rule defines BSER as on-site "inside the fenceline," heat-rate efficiency improvements. Under the ACE rule, states have the primary role in developing standards of performance that result from the application of BSER. States have three years to develop and submit compliance plans to the EPA. The EPA will have a year to review and approve those plans. States are then given 24 months from the approval date to implement the plan and can extend the compliance schedule for units that meet progress milestones. The ACE rule will apply to Columbia and the Elm Road Units. MGE is currently evaluating how this rule may impact operations and monitoring state activity on BSER development. Until the State of Wisconsin develops a plan that is accepted by the EPA, MGE will not be able to determine the final impact of the rule. Additionally, the ACE rule and repeal of the Clean Power Plan are subject to a legal challenge pending in the United States District Court of the District of Columbia. MGE will continue to evaluate the plan development within the state and monitor ongoing and potential legal proceedings associated with the ACE rule. •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 that 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). The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and fine particulate (PM2.5) air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. In September 2019, the U.S. Court of Appeals upheld the legal argument that the EPA cannot provide a partial remedy to the Clean Air Act's "Good Neighbor Provision," which addresses interstate transport of pollutants from upwind states to downwind states. Wisconsin is considered an upwind state under CSAPR and is potentially impacted by rules that the EPA will develop to address this remand. MGE has met its current CSAPR obligations through a combination of reduced emissions through pollution control (e.g., SCR installation at Columbia), as well as owned, received, and purchased allowances. While uncertainty remains around CSAPR due to legal challenges, MGE expects that it will meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor developments in EPA revisions after the remand and any ongoing litigation over 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 developed a compliance plan. Columbia's operator is also exploring alternative compliance options to meet the rule requirements by the rule's deadline. MGE will continue to monitor the operator's plans for compliance to assess potential impacts on operations. In December 2019, the EPA introduced a proposed rule to revise some of the closure standards that are in the 2015 CCR Rule. If the proposed rule is finalized MGE does not anticipate that it will have a material impact on our 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 accrues for 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

3 Months Ended

Mar. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

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 operations are conducted, the costs of 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 could 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. MGE is currently evaluating proposed rule modifications for applicability to the Columbia and Elm Road Units. Until the modifications are finalized, MGE will not know with certainty how operations will be impacted.

•The EPA's cooling water intake rules, which require cooling water intake structures at electric power plants to meet best available technology (BAT) 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 will need to conduct studies at its Blount plant by the end of 2021 to determine BAT. Columbia's operators will also need to determine BAT. Future BAT requirements at Blount and Columbia will be based on the results of these intake studies and will be specified in the next permits expected to be issued in 2023 or later. MGE expects that this 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 2019, the EPA published a final rule creating the Affordable Clean Energy (ACE) rule to reduce greenhouse gas emissions from existing coal-fired EGUs. The ACE rule 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 coal-fired EGUs over 25 MW. The ACE rule defines BSER as on-site "inside the fenceline," heat-rate efficiency improvements. Under the ACE rule, states have the primary role in developing standards of performance that result from the application of BSER. States have three years to develop and submit compliance plans to the EPA. The EPA will have a year to review and approve those plans. States are then given 24 months from the approval date to implement the plan and can extend the compliance schedule for units that meet progress milestones.

The ACE rule will apply to Columbia and the Elm Road Units. MGE is currently evaluating how this rule may impact operations and monitoring state activity on BSER development. Until the State of Wisconsin develops a plan that is accepted by the EPA, MGE will not be able to determine the final impact of the rule. Additionally, the ACE rule and repeal of the Clean Power Plan are subject to a legal challenge pending in the United States District Court of the District of Columbia. MGE will continue to evaluate the plan development within the state and monitor ongoing and potential legal proceedings associated with the ACE rule.

•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 that 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).

The EPA's CSAPR and its progeny are a suite of interstate air pollution transport rules designed to reduce ozone and fine particulate (PM2.5) air levels in areas that the EPA has determined as being significantly impacted by pollution from upwind states. In September 2019, the U.S. Court of Appeals upheld the legal argument that the EPA cannot provide a partial remedy to the Clean Air Act's "Good Neighbor Provision," which addresses interstate transport of pollutants from upwind states to downwind states. Wisconsin is considered an upwind state under CSAPR and is potentially impacted by rules that the EPA will develop to address this remand. MGE has met its current CSAPR obligations through a combination of reduced emissions through pollution control (e.g., SCR installation at Columbia), as well as owned, received, and purchased allowances. While uncertainty remains around CSAPR due to legal challenges, MGE expects that it will meet ongoing CSAPR obligations for the foreseeable future. MGE will continue to monitor developments in EPA revisions after the remand and any ongoing litigation over 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 developed a compliance plan. Columbia's operator is also exploring alternative compliance options to meet the rule requirements by the rule's deadline. MGE will continue to monitor the operator's plans for compliance to assess potential impacts on operations.

In December 2019, the EPA introduced a proposed rule to revise some of the closure standards that are in the 2015 CCR Rule. If the proposed rule is finalized MGE does not anticipate that it will have a material impact on our 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 accrues for 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.