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Pension and Other Postretirement Benefit Plans (Details) - USD ($) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2018 | Jun. 30, 2018 | Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Other (deductions) | $ 5,868,000 | $ 5,042,000 |  | $ 7,243,000 | $ 10,663,000
Other income | 4,796,000 | 3,450,000 |  | 8,265,000 | 8,351,000
PNM |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Other (deductions) | 3,768,000 | 4,566,000 |  | 5,229,000 | 9,526,000
Other income | 2,292,000 | 2,665,000 |  | 4,684,000 | 6,508,000
PNM | Pension Plan |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |
Service cost | 0 | 0 |  | 0 | 0
Interest cost | 6,068,000 | 6,727,000 |  | 12,135,000 | 13,454,000
Expected return on plan assets | (8,672,000) | (8,451,000) |  | (17,343,000) | (16,901,000)
Amortization of net (gain) loss | 4,087,000 | 4,001,000 |  | 8,174,000 | 8,003,000
Amortization of prior service cost | (241,000) | (241,000) |  | (483,000) | (483,000)
Net Periodic Benefit Cost | 1,242,000 | 2,036,000 |  | 2,483,000 | 4,073,000
Contributions by employer |  |  |  | 0 | 0
Total expected employer contributions for future fiscal years | 0 |  |  | 0 |
Expected employer contributions in year 5 | 5,500,000 |  |  | $ 5,500,000 |
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 |  | $ 41,000 | 48,000
Interest cost | 860,000 | 1,006,000 |  | 1,720,000 | 2,013,000
Expected return on plan assets | (1,353,000) | (1,308,000) |  | (2,707,000) | (2,615,000)
Amortization of net (gain) loss | 588,000 | 921,000 |  | 1,177,000 | 1,841,000
Amortization of prior service cost | (416,000) | (416,000) |  | (832,000) | (832,000)
Net Periodic Benefit Cost | (300,000) | 227,000 |  | (601,000) | 455,000
Contributions by employer |  |  |  | 0 | 0
PNM | Executive Retirement Program |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |
Service cost | 0 | 0 |  | 0 | 0
Interest cost | 155,000 | 174,000 |  | 311,000 | 349,000
Expected return on plan assets | 0 | 0 |  | 0 | 0
Amortization of net (gain) loss | 90,000 | 78,000 |  | 179,000 | 157,000
Amortization of prior service cost | 0 | 0 |  | 0 | 0
Net Periodic Benefit Cost | 245,000 | 252,000 |  | 490,000 | 506,000
Contributions by employer | 400,000 | 400,000 |  | 900,000 | 900,000
Total expected employer contributions for fiscal year | 1,600,000 |  |  | 1,600,000 |
Estimated employer contributions in Year 2-5 | 5,700,000 |  |  | 5,700,000 |
TNMP |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Other (deductions) | 1,391,000 | 109,000 |  | 1,060,000 | 198,000
Other income | 2,223,000 | 541,000 |  | 2,976,000 | 1,363,000
TNMP | Pension Plan |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |
Service cost | 0 | 0 |  | 0 | 0
Interest cost | 656,000 | 722,000 |  | 1,312,000 | 1,443,000
Expected return on plan assets | (991,000) | (945,000) |  | (1,981,000) | (1,889,000)
Amortization of net (gain) loss | 272,000 | 231,000 |  | 544,000 | 461,000
Amortization of prior service cost | 0 | 0 |  | 0 | 0
Net Periodic Benefit Cost | (63,000) | 8,000 |  | (125,000) | 15,000
Contributions by employer |  |  |  | 0 | 0
Estimated employer contributions in Year 2-5 | 0 |  |  | $ 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 |  | $ 67,000 | 72,000
Interest cost | 119,000 | 139,000 |  | 238,000 | 278,000
Expected return on plan assets | (135,000) | (114,000) |  | (271,000) | (228,000)
Amortization of net (gain) loss | (56,000) | (20,000) |  | (113,000) | (40,000)
Amortization of prior service cost | 0 | 0 |  | 0 | 0
Net Periodic Benefit Cost | (39,000) | 41,000 |  | (79,000) | 82,000
Contributions by employer | 0 | 0 |  | 300,000 | 700,000
Estimated employer contributions in Year 2-5 | 1,400,000 |  |  | 1,400,000 |
TNMP | Executive Retirement Program |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |
Service cost | 0 | 0 |  | 0 | 0
Interest cost | 7,000 | 8,000 |  | 15,000 | 17,000
Expected return on plan assets | 0 | 0 |  | 0 | 0
Amortization of net (gain) loss | 4,000 | 2,000 |  | 8,000 | 4,000
Amortization of prior service cost | 0 | 0 |  | 0 | 0
Net Periodic Benefit Cost | 11,000 | 10,000 |  | 23,000 | 21,000
Total expected employer contributions for fiscal year | 100,000 |  |  | 100,000 |
Estimated employer contributions in Year 2-5 | 400,000 |  |  | 400,000 |
TNMP | Executive Retirement Program | Maximum |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |
Contributions by employer | 100,000 | 100,000 |  | 100,000 | 100,000
Accounting Standards Update 2017-07 |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Other (deductions) |  | $ 2,100,000 |  |  | $ 4,300,000
Accounting Standards Update 2017-07 | PNM |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Other (deductions) | 1,200,000 |  |  | 2,100,000 |
Non-service cost deferred as regulatory assets | 100,000 |  |  | 300,000 |
Accounting Standards Update 2017-07 | TNMP |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Other income | 100,000 |  |  | 300,000 |
Non-service cost deferred as regulatory liability | $ 100,000 |  |  | $ 100,000 |
Forecast | TNMP | OPEB Plan |  |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |  |
Contributions by employer |  |  | $ 0 |  |

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