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COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) $ in Millions | 1 Months Ended | 9 Months Ended | 15 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2021 area | Mar. 31, 2021 States | Dec. 31, 2020 USD ($) performance_obligations micrograms | Sep. 30, 2021 USD ($) performance_obligations MW | Mar. 31, 2019 MW | Feb. 28, 2021 compliance_option
Manufactured gas plant remediation |  |  |  |  |  |
Regulatory assets |  |  | $ 3,544.1 | $ 3,628.1 |  |
Environmental remediation costs |  |  |  |  |  |
Manufactured gas plant remediation |  |  |  |  |  |
Regulatory assets |  |  | $ 638.2 | $ 601.9 |  |
National Ambient Air Quality Standards | Electric |  |  |  |  |  |
Air quality |  |  |  |  |  |
Number of changes to the 2015 ozone standards | performance_obligations |  |  | 0 |  |  |
Number of counties to have boundaries revised | area | 13 |  |  |  |  |
Number of nonattainment areas as designated by the EPA | area | 6 |  |  |  |  |
Number of revisions necessary to meet the 2012 standard for particulate matter | performance_obligations |  |  | 0 |  |  |
Current number of micrograms per cubic meter that particulate matter needs to be below | micrograms |  |  | 12 |  |  |
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 emissions reduction below 2005 levels by 2025 |  |  |  | 60.00% |  |
Company goal for percentage of carbon 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 |  |  |  | 1,600 |  |
Climate Change | Natural gas |  |  |  |  |  |
Air quality |  |  |  |  |  |
Initial 2030 percentage goal for a reduction of methane emissions from a 2011 baseline |  |  |  | 30.00% |  |
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 | States |  | 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 | 510.3 |  |
Manufactured Gas Plant Remediation | Natural gas | Environmental remediation costs |  |  |  |  |  |
Manufactured gas plant remediation |  |  |  |  |  |
Regulatory assets |  |  | $ 638.2 | $ 601.9 |  |

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