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Regulatory Matters - Ohio (Details) - OHIO - PUCO - USD ($) $ in Millions |  |  |  |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Nov. 24, 2020 | Jul. 15, 2019 | Nov. 09, 2018 | Jun. 01, 2016 | Mar. 31, 2021 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2020
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Proposed goal to reduce CO2 pollution (percent) |  |  |  | 90.00% |  |  |  |
Energy Conservation, Economic Development and Job Retention |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Contribution amount |  |  |  | $ 51.0 |  |  |  |
Distribution Modernization Rider |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Annual revenue cap for rider |  |  |  |  |  |  | $ 132.5 |
Recovery period |  |  |  |  |  |  | 3 years |
Approved amount for rider |  |  |  |  |  | $ 168.0 | $ 168.0 |
Requested plan extension period | 2 years |  |  |  |  |  |  |
Delivery Capital Recovery Rider |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Annual revenue cap for rider for years three through six |  |  |  | 20.0 |  |  |  |
Annual revenue cap for rider for years six through eight |  |  |  | $ 15.0 |  |  |  |
OCC DMR Refund | The Ohio Companies |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Loss contingency, damages sought |  | $ 42.0 |  |  |  |  |  |
Distribution Platform Modernization Plan |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Approved amount of annual increase (decrease) |  |  | $ 516.0 |  |  |  |  |
Period of grid modernization plan |  |  | 3 years |  |  |  |  |
Decoupling Rider | The Ohio Companies |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Amount of refunds announced |  |  |  |  | $ 27.0 |  |  |
Rider CSR | The Ohio Companies |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |
Pre-tax impairment of regulatory asset |  |  |  |  |  |  |  | $ 108.0
Impairment of regulatory asset, net |  |  |  |  |  |  |  | 84.0
Lost distribution revenue |  |  |  |  |  |  |  | $ 77.0

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