Pension and Other Postretirement Benefit Plans (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	20,181,000	22,731,000
Expected return on plan assets	(8,451,000)	(8,854,000)	(25,352,000)	(26,562,000)
Amortization of net (gain) loss	4,001,000	3,455,000	12,004,000	10,365,000
Amortization of prior service cost	(241,000)	(241,000)	(724,000)	(724,000)
Net Periodic Benefit Cost	2,036,000	1,937,000	6,109,000	5,810,000
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	$ 72,000	105,000
Interest cost	1,006,000	1,087,000	3,019,000	3,260,000
Expected return on plan assets	(1,308,000)	(1,371,000)	(3,923,000)	(4,113,000)
Amortization of net (gain) loss	921,000	286,000	2,762,000	858,000
Amortization of prior service cost	(416,000)	(7,000)	(1,248,000)	(22,000)
Net Periodic Benefit Cost	227,000	30,000	682,000	88,000
Contributions by employer	0	800,000	0	2,400,000
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	523,000	609,000
Expected return on plan assets	0	0	0	0
Amortization of net (gain) loss	78,000	64,000	235,000	192,000
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	252,000	267,000	758,000	801,000
Contributions by employer	400,000	400,000	1,200,000	1,200,000
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	2,165,000	2,478,000
Expected return on plan assets	(945,000)	(986,000)	(2,834,000)	(2,957,000)
Amortization of net (gain) loss	231,000	175,000	692,000	525,000
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	8,000	15,000	23,000	46,000
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	$ 107,000	139,000
Interest cost	139,000	169,000	417,000	508,000
Expected return on plan assets	(114,000)	(122,000)	(342,000)	(367,000)
Amortization of net (gain) loss	(20,000)	(10,000)	(60,000)	(30,000)
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	41,000	83,000	122,000	250,000
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	25,000	30,000
Expected return on plan assets	0	0	0	0
Amortization of net (gain) loss	2,000	1,000	7,000	1,000
Amortization of prior service cost	0	0	0	0
Net Periodic Benefit Cost	10,000	11,000	32,000	31,000
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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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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