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Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations [Line Items]
ARO liabilities related to nuclear decommissioning	80.00%
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 127,519	$ 111,895	$ 104,170
Liabilities incurred	1,854	0	0
Liabilities settled	(968)	(14)	(730)
Accretion expense	10,680	9,170	8,625
Revisions to estimated cash flows	7,594	6,468	(170)
Ending balance	146,679	127,519	111,895
Public Service Company of New Mexico
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	126,601	111,049	103,182
Liabilities incurred	1,853	0	0
Liabilities settled	(944)	(14)	(506)
Accretion expense	10,603	9,098	8,543
Revisions to estimated cash flows	7,594	6,468	(170)
Ending balance	145,707	126,601	111,049
Texas-New Mexico Power Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	754	695	848
Liabilities incurred	0	0	0
Liabilities settled	(24)	0	(224)
Accretion expense	63	59	71
Revisions to estimated cash flows	0	0	0
Ending balance	$ 793	$ 754	$ 695

X

- Definition

Asset Retirement Obligation, Liabilities Related to Nuclear Decommissioning

+ References

No definition available.

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- Definition

Asset Retirement Obligations [Line Items]

+ References

No definition available.

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

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- Definition

Amount of asset retirement obligations incurred during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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