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Regulatory and Rate Matters (Tables) | 6 Months Ended
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Jun. 30, 2021
Regulated Operations [Abstract] |
Schedule of Rate Increases for Transmission Costs | The following sets forth TNMP’s recent interim transmission cost rate increases:
Effective Date |  | Approved Increase in Rate Base |  | Annual Increase in Revenue
|  | (In millions)
March 27, 2020 |  | $ | 59.2 |  |  | $ | 7.8 |
October 7, 2020 |  | 10.8 |  |  | 2.0 |
March 12, 2021 |  | 112.6 |  |  | 14.1 |

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