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Pension and Other Postretirement Benefit Plans (Details) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |  |  |
Other (deductions) | $ 1,376,000 | $ 5,621,000 |
Regulatory assets | 595,398,000 |  | $ 600,672,000
Other income | 3,469,000 | 4,902,000 |
Regulatory liabilities | 934,053,000 |  | 933,578,000
PNM |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Other (deductions) | 1,462,000 | 4,959,000 |
Regulatory assets | 453,912,000 |  | 459,239,000
Other income | 2,391,000 | 3,843,000 |
Regulatory liabilities | 749,319,000 |  | 754,441,000
PNM | Pension Plan |  |  |
Components of Net Periodic Benefit Cost |  |  |
Service cost | 0 | 0 |
Interest cost | 6,068,000 | 6,727,000 |
Expected return on plan assets | (8,672,000) | (8,451,000) |
Amortization of net (gain) loss | 4,087,000 | 4,001,000 |
Amortization of prior service cost | (241,000) | (241,000) |
Net Periodic Benefit Cost | 1,242,000 | 2,036,000 |
Contributions by employer | 0 | 0 |
Total expected employer contributions for future fiscal years | 0 |  |
Expected employer contributions in year 5 | $ 5,100,000 |  |
PNM | Pension Plan | Minimum |  |  |
Components of Net Periodic Benefit Cost |  |  |
Assumptions used calculating net periodic benefit cost, discount rate | 4.00% |  |
PNM | Pension Plan | Maximum |  |  |
Components of Net Periodic Benefit Cost |  |  |
Assumptions used calculating net periodic benefit cost, discount rate | 5.10% |  |
PNM | OPEB Plan |  |  |
Components of Net Periodic Benefit Cost |  |  |
Service cost | $ 21,000 | 24,000 |
Interest cost | 860,000 | 1,006,000 |
Expected return on plan assets | (1,353,000) | (1,308,000) |
Amortization of net (gain) loss | 588,000 | 921,000 |
Amortization of prior service cost | (416,000) | (416,000) |
Net Periodic Benefit Cost | (300,000) | 227,000 |
Contributions by employer | 0 |  |
Estimated employer contributions in Year 2-5 | 0 |  |
PNM | Executive Retirement Program |  |  |
Components of Net Periodic Benefit Cost |  |  |
Service cost | 0 | 0 |
Interest cost | 155,000 | 174,000 |
Expected return on plan assets | 0 | 0 |
Amortization of net (gain) loss | 90,000 | 78,000 |
Amortization of prior service cost | 0 | 0 |
Net Periodic Benefit Cost | 245,000 | 252,000 |
Contributions by employer | 500,000 | 500,000 |
Total expected employer contributions for fiscal year | 1,500,000 |  |
Estimated employer contributions in Year 2-5 | 5,700,000 |  |
TNMP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Other (deductions) | (331,000) | 90,000 |
Regulatory assets | 141,486,000 |  | 141,433,000
Other income | 754,000 | 822,000 |
Regulatory liabilities | 184,734,000 |  | $ 179,137,000
TNMP | Pension Plan |  |  |
Components of Net Periodic Benefit Cost |  |  |
Service cost | 0 | 0 |
Interest cost | 656,000 | 722,000 |
Expected return on plan assets | (991,000) | (945,000) |
Amortization of net (gain) loss | 272,000 | 231,000 |
Amortization of prior service cost | 0 | 0 |
Net Periodic Benefit Cost | (63,000) | 8,000 |
Contributions by employer | 0 | 0 |
Estimated employer contributions in Year 2-5 | $ 0 |  |
TNMP | Pension Plan | Minimum |  |  |
Components of Net Periodic Benefit Cost |  |  |
Assumptions used calculating net periodic benefit cost, discount rate | 4.00% |  |
TNMP | Pension Plan | Maximum |  |  |
Components of Net Periodic Benefit Cost |  |  |
Assumptions used calculating net periodic benefit cost, discount rate | 5.10% |  |
TNMP | OPEB Plan |  |  |
Components of Net Periodic Benefit Cost |  |  |
Service cost | $ 33,000 | 36,000 |
Interest cost | 119,000 | 139,000 |
Expected return on plan assets | (135,000) | (114,000) |
Amortization of net (gain) loss | (56,000) | (20,000) |
Amortization of prior service cost | 0 | 0 |
Net Periodic Benefit Cost | (39,000) | 41,000 |
Contributions by employer | 300,000 | 700,000 |
Estimated employer contributions in Year 2-5 | 1,400,000 |  |
TNMP | Executive Retirement Program |  |  |
Components of Net Periodic Benefit Cost |  |  |
Service cost | 0 | 0 |
Interest cost | 7,000 | 8,000 |
Expected return on plan assets | 0 | 0 |
Amortization of net (gain) loss | 4,000 | 2,000 |
Amortization of prior service cost | 0 | 0 |
Net Periodic Benefit Cost | 11,000 | 10,000 |
Total expected employer contributions for fiscal year | 100,000 |  |
Estimated employer contributions in Year 2-5 | 400,000 |  |
TNMP | Executive Retirement Program | Maximum |  |  |
Components of Net Periodic Benefit Cost |  |  |
Contributions by employer | 100,000 | 100,000 |
Accounting Standards Update 2017-07 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Other (deductions) |  | $ 2,100,000 |
Accounting Standards Update 2017-07 | PNM |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Other (deductions) | 900,000 |  |
Regulatory assets | 300,000 |  |
Accounting Standards Update 2017-07 | TNMP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Other income | 100,000 |  |
Regulatory liabilities | $ 100,000 |  |

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