Regulatory and Rate Matters - Energy Efficiency and Load Management (Details) - Public Service Company of New Mexico [Member] $ in Millions				1 Months Ended			12 Months Ended
	Sep. 29, 2016 USD ($)	Apr. 15, 2016 USD ($) GWh program	Oct. 06, 2014 USD ($)	Jan. 31, 2015 USD ($)	Nov. 30, 2013	Oct. 31, 2012 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2016	Jan. 30, 2015 USD ($)
Energy Efficiency and Load Management [Member] | Disincentives/Incentives Added [Member]
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency						$ 22.5
Authorization to recover an incentive equal to a percentage of annual program costs					7.60%
Annual incentive								$ 1.7
2014 Energy Efficiency and Load Management Program [Member] | Disincentives/Incentives Added [Member]
Public Utilities, General Disclosures [Line Items]
Program costs related to energy efficiency			$ 25.8
Proposed energy efficiency incentive							$ 2.1
Anticipated future profit incentive 2015										$ 1.7
Anticipated future profit incentive 2016										$ 1.8
2017 Energy Efficiency and Load Management Program [Member] | Disincentives/Incentives Added [Member]
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			$ 1.8
Maximum [Member] | Renewable Portfolio Standard [Member]
Public Utilities, General Disclosures [Line Items]
Reasonable cost threshold	3.00%							3.00%
Sliding scale profit incentive	9.00%
Minimum [Member] | Renewable Portfolio Standard [Member]
Public Utilities, General Disclosures [Line Items]
Reasonable cost threshold									3.00%
Sliding scale profit incentive	7.10%