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Regulatory and Rate Matters - Energy Efficiency and Load Management (Details) $ in Millions								12 Months Ended
	Apr. 13, 2018 USD ($)	Nov. 08, 2017 USD ($)	Jul. 26, 2017 USD ($) GWh	Jun. 21, 2017	Apr. 14, 2017 USD ($) GWh	Jan. 11, 2017 USD ($)	Apr. 15, 2016 USD ($) GWh program	Dec. 31, 2018 USD ($)	Nov. 07, 2017	Dec. 31, 2013
Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Frequency of energy efficiency plan filings				3 years
Percentage of modification to funding levels				0.1
Public Service Company of New Mexico | 2017 Energy Efficiency and Load Management Program | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency						$ 26.0	$ 28.0
Number of energy efficiency and load management programs (in programs) | program							10
Application of incentive based on target savings							$ 2.4
Energy efficiency targeted savings (in gwh) | GWh							75
Minimum profit incentive						$ 1.8
Public Service Company of New Mexico | Energy Efficiency and Load Management Program, Proposed 2018 Portfolio | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency		$ 23.6			$ 25.1
Application of incentive based on target savings					$ 1.9
Energy efficiency targeted savings (in gwh) | GWh					53
Projected earned incentive	$ 2.3		$ 1.9		$ 2.1			$ 2.7
Targeted energy savings | GWh			69		70
Public Service Company of New Mexico | Energy Efficiency and Load Management Program, Proposed 2019 Portfolio | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency		$ 24.9			$ 28.2
Application of incentive based on target savings			$ 1.7		$ 2.1			$ 1.8
Public Service Company of New Mexico | Maximum | Renewable Portfolio Standard
Public Utilities, General Disclosures [Line Items]
Reasonable cost threshold						3.00%				3.00%
Sliding scale profit incentive						9.00%
Public Service Company of New Mexico | Minimum | Renewable Portfolio Standard
Public Utilities, General Disclosures [Line Items]
Reasonable cost threshold								3.00%
Sliding scale profit incentive						7.10%
Measurement Input, Discount Rate
Public Utilities, General Disclosures [Line Items]
Tax-adjusted WACC		0.0959							0.0771

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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