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COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) T in Millions, $ in Millions | 3 Months Ended | 12 Months Ended | 15 Months Ended
--- | --- | --- | ---
Mar. 31, 2021 USD ($) States performance_obligations compliance_option MW | Dec. 31, 2020 USD ($) T | Mar. 31, 2019 MW
Manufactured gas plant remediation |  |  |
Regulatory assets | $ 3,793.8 | $ 3,544.1 |
Environmental remediation costs |  |  |
Manufactured gas plant remediation |  |  |
Regulatory assets | $ 623.1 | $ 638.2 |
National Ambient Air Quality Standards | Electric |  |  |
Air quality |  |  |
Number of changes to the 2015 ozone standards | performance_obligations | 0 |  |
Number of revisions necessary to the 2012 standard for particulate matter | performance_obligations | 0 |  |
Climate Change | Electric |  |  |
Air quality |  |  |
Number of rules that regulate GHG emissions from electric generating units | compliance_option | 0 |  |
Company goal percentage met by the end of 2020 for carbon dioxide emissions reduction below 2005 levels | 50.00% |  |
Company goal for percentage of carbon dioxide emissions reduction below 2005 levels by 2025 | 60.00% |  |
Company goal for percentage of carbon dioxide emissions reduction below 2005 levels by 2030 | 80.00% |  |
Capacity of coal-fired generation retired, in megawatts | MW |  |  | 1,800
Capacity of fossil-fueled generation to be retired by 2025, in megawatts | MW | 1,800 |  |
Carbon dioxide emissions | T |  | 20.1 |
Climate Change | Natural gas |  |  |
Air quality |  |  |
Initial 2030 percentage goal for a reduction of methane emissions from a 2011 baseline | 30.00% |  |
Carbon dioxide emissions | T |  | 27.0 |
Cross State Air Pollution Rule Update Rule Revision | Electric |  |  |
Air quality |  |  |
Number of states in Group 2 for CSAPR update rule revision | States | 9 |  |
Number of states affected by the CSAPR update rule revision | States | 21 |  |
Amount of further NOx reductions needed within the nine effected states | performance_obligations | 0 |  |
Steam Electric Effluent Limitation Guidelines | Electric |  |  |
Water quality |  |  |
Number of new ELG rule requirements that affect our electric utilities | performance_obligations | 2 |  |
Expected capital investment to achieve required discharge limits | $ 110.0 |  |
Manufactured Gas Plant Remediation | Natural gas |  |  |
Manufactured gas plant remediation |  |  |
Reserves for future environmental remediation | 532.9 | $ 532.9 |
Manufactured Gas Plant Remediation | Natural gas | Environmental remediation costs |  |  |
Manufactured gas plant remediation |  |  |
Regulatory assets | $ 623.1 | $ 638.2 |

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