Pension and Other Postretirement Benefit Plans (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
PNM \| Pension Plan
Components of Net Periodic Benefit Cost
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	6,727,000	7,577,000	13,454,000	15,154,000
Expected return on plan assets	(8,451,000)	(8,854,000)	(16,901,000)	(17,708,000)
Amortization of net (gain) loss	4,001,000	3,455,000	8,003,000	6,910,000
Amortization of prior service cost	(241,000)	(241,000)	(483,000)	(483,000)
Net Periodic Benefit Cost	2,036,000	1,937,000	4,073,000	3,873,000
Contributions by employer	0	0	0	0
Total expected employer contributions for future fiscal years	0		$ 0
PNM \| Pension Plan \| Minimum
Components of Net Periodic Benefit Cost
Assumptions used calculating net periodic benefit cost, discount rate			4.10%
PNM \| Pension Plan \| Maximum
Components of Net Periodic Benefit Cost
Assumptions used calculating net periodic benefit cost, discount rate			4.90%
PNM \| OPEB Plan
Components of Net Periodic Benefit Cost
Service cost	24,000	35,000	$ 48,000	70,000
Interest cost	1,006,000	1,087,000	2,013,000	2,173,000
Expected return on plan assets	(1,308,000)	(1,371,000)	(2,615,000)	(2,742,000)
Amortization of net (gain) loss	921,000	286,000	1,841,000	572,000
Amortization of prior service cost	(416,000)	(7,000)	(832,000)	(15,000)
Net Periodic Benefit Cost	227,000	30,000	455,000	58,000
Contributions by employer	0	800,000	0	1,600,000
Total expected employer contributions for future fiscal years	0		0
PNM \| Executive Retirement Program
Components of Net Periodic Benefit Cost
Service cost	0	0	0	0
Interest cost	174,000	203,000	349,000	406,000
Expected return on plan assets	0	0	0	0
Amortization of net (gain) loss	78,000	64,000	157,000	128,000
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	252,000	267,000	506,000	534,000
Contributions by employer	400,000	400,000	900,000	900,000
Total expected employer contributions for future fiscal years	5,800,000		5,800,000
Total expected employer contributions for fiscal year	1,500,000		1,500,000
Texas-New Mexico Power Company \| Pension Plan
Components of Net Periodic Benefit Cost
Service cost	0	0	0	0
Interest cost	722,000	826,000	1,443,000	1,652,000
Expected return on plan assets	(945,000)	(986,000)	(1,889,000)	(1,971,000)
Amortization of net (gain) loss	231,000	175,000	461,000	350,000
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	8,000	15,000	15,000	31,000
Contributions by employer	0	0	0	0
Total expected employer contributions for future fiscal years	0		$ 0
Texas-New Mexico Power Company \| Pension Plan \| Minimum
Components of Net Periodic Benefit Cost
Assumptions used calculating net periodic benefit cost, discount rate			4.10%
Texas-New Mexico Power Company \| Pension Plan \| Maximum
Components of Net Periodic Benefit Cost
Assumptions used calculating net periodic benefit cost, discount rate			4.90%
Texas-New Mexico Power Company \| OPEB Plan
Components of Net Periodic Benefit Cost
Service cost	36,000	46,000	$ 72,000	93,000
Interest cost	139,000	169,000	278,000	339,000
Expected return on plan assets	(114,000)	(122,000)	(228,000)	(245,000)
Amortization of net (gain) loss	(20,000)	(10,000)	(40,000)	(20,000)
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	41,000	83,000	82,000	167,000
Contributions by employer	0	0	700,000	0
Total expected employer contributions for future fiscal years	1,400,000		1,400,000
Total expected employer contributions for fiscal year	0		0
Texas-New Mexico Power Company \| Executive Retirement Program
Components of Net Periodic Benefit Cost
Service cost	0	0	0	0
Interest cost	8,000	10,000	17,000	20,000
Expected return on plan assets	0	0	0	0
Amortization of net (gain) loss	2,000	1,000	4,000	1,000
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	10,000	11,000	21,000	21,000
Total expected employer contributions for future fiscal years	400,000		400,000
Total expected employer contributions for fiscal year	100,000		100,000
Texas-New Mexico Power Company \| Executive Retirement Program \| Maximum
Components of Net Periodic Benefit Cost
Contributions by employer	$ 100,000	$ 100,000	$ 100,000	$ 100,000

Defined Benefit Plan, Estimated Future Employer Contributions in Year Two Through Year Five

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Defined Benefit Plan Total Expected Employer Contributions for Fiscal Year

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- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

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Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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- Definition

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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