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Regulatory and Rate Matters - Energy Efficiency and Load Management (Details) $ in Millions	Nov. 08, 2017 USD ($)	Nov. 07, 2017	Jul. 26, 2017 USD ($) GWh	Apr. 14, 2017 USD ($) GWh	Jan. 11, 2017 USD ($)	Apr. 15, 2016 USD ($) GWh program	Oct. 06, 2014 USD ($)	Dec. 31, 2017	Dec. 31, 2013
Public Utilities, General Disclosures [Line Items]
Tax-adjusted WACC	9.59%	7.71%
Public Service Company of New Mexico | 2014 Energy Efficiency and Load Management Program | Disincentives/Incentives Added
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency							$ 25.8
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			$ 1.9	$ 2.1
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
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%

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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