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Regulatory and Rate Matters Regulatory and Rate Matters (Tables) | 12 Months Ended
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Dec. 31, 2018
Regulated Operations [Abstract] |
Schedule of Energy/Capacity Transactions | Information about PNM’s purchases and sales is as follows:
| Sales |  | Purchases
| GWh |  | Amount |  | GWh |  | Amount
|  |  | (In millions) |  |  |  | (In millions)
Year ended December 31, 2018 | 725.7 |  |  | $ | 25.8 |  |  | 822.7 |  |  | $ | 28.7 |
Year ended December 31, 2017 | 827.1 |  |  | 23.6 |  |  | 849.0 |  |  | 24.2 |
Year ended December 31, 2016 | 482.3 |  |  | 12.8 |  |  | 484.6 |  |  | 12.9 |
Schedule of Rate Increases for Transmission Costs | TNMP recovers the costs of its energy efficiency programs through an energy efficiency cost recovery factor (“EECRF”), which includes projected program costs, under or over collected costs from prior years, rate case expenses, and performance bonuses (if the programs exceed mandated savings goals). The following sets forth TNMP’s approved EECRF increases:
Effective Date |  | Aggregate Collection Amount |  | Performance Bonus
|  | (In millions)
March 1, 2016 |  | $ | 6.0 |  |  | $ | 0.7 |
March 1, 2017 |  | 6.0 |  |  | 0.8 |
March 1, 2018 |  | 6.0 |  |  | 1.1 |
March 1, 2019 |  | 5.6 |  |  | 0.8 |
TNMP can update its transmission cost of service (“TCOS”) rates twice per year to reflect changes in its invested capital although updates are not allowed while a general rate case is in process. Updated rates reflect the addition and retirement of transmission facilities, including appropriate depreciation, federal income tax and other associated taxes, and the approved rate of return on such facilities. 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 23, 2016 |  | $ | 25.8 |  |  | $ | 4.3 |
September 8, 2016 |  | 9.5 |  |  | 1.8 |
March 14, 2017 |  | 30.2 |  |  | 4.8 |
September 13, 2017 |  | 27.5 |  |  | 4.7 |
March 27, 2018 |  | 32.0 |  |  | 0.6 |

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