Regulatory and Rate Matters (Details)																1 Months Ended				3 Months Ended		6 Months Ended								12 Months Ended								14 Months Ended
	Jan. 29, 2016 USD ($)	Nov. 30, 2015	Aug. 27, 2015 USD ($)	Jul. 31, 2015	May. 27, 2015	Mar. 20, 2015 USD ($)	Feb. 17, 2015	Dec. 11, 2014 USD ($)	Oct. 06, 2014 USD ($)	Apr. 30, 2014 USD ($)	Apr. 23, 2014 USD ($)	May. 28, 2013	Mar. 01, 2013	Jan. 02, 2013 USD ($)	Dec. 06, 2012 USD ($)	Nov. 30, 2013	Oct. 31, 2012 USD ($)	Jul. 31, 2011 USD ($)	Oct. 31, 2010 USD ($)	Jun. 30, 2015 USD ($) MW	Dec. 31, 2013 USD ($) MW	Mar. 09, 2016 USD ($)	Sep. 09, 2015 USD ($)	Mar. 15, 2015 USD ($)	Sep. 07, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 12, 2014 USD ($)	Sep. 16, 2013 USD ($)	Mar. 19, 2013 USD ($)	Dec. 31, 2017 MW	Feb. 28, 2017 USD ($)	Feb. 29, 2016 USD ($)	Dec. 31, 2015 USD ($) MW	Feb. 28, 2015 USD ($)	Dec. 31, 2014 USD ($) MWh MW	Dec. 31, 2013 USD ($) MW	Dec. 31, 2012 USD ($)	Feb. 28, 2014 USD ($)	Feb. 19, 2016 customer	Oct. 02, 2015 USD ($)	Jan. 30, 2015 USD ($)	Jun. 20, 2014 USD ($) customer
Public Service Company of New Mexico [Member] | San Juan Generating Station Units 2 and 3 [Member] | Clean Air Act, SNCR [Member]
Rate Matters [Line Items]
Newly-identified replacement gas plant (in megawatts) | MW																				187													85
Cost of replacement gas-generation																				$ 133,200,000													$ 101,800,000
Public Service Company of New Mexico [Member] | Four Corners [Member]
Rate Matters [Line Items]
Jointly owned utility plant, ownership percentage							7.00%
Period of time to file a waiver of rights of first refusal							120 days
Public Service Company of New Mexico [Member] | 2014 Electric Rate Case [Member]
Rate Matters [Line Items]
Requested rate increase (decrease)								$ 107,400,000
Future test year period, period of time following the filing of an application					45 days
Future test year period, Number of days following the filing of application for rate increase, Alternative interpretation					13 months
Requested stay period				30 days
Future test year period, Revised, Number of days following the filing of application for rate increase		13 months
Public Service Company of New Mexico [Member] | 2015 Electric Rate Case [Member]
Rate Matters [Line Items]
Requested rate increase (decrease)			$ 123,500,000
Requested return on equity			10.50%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member]
Rate Matters [Line Items]
Solar photovoltaic capacity (in megawatts) | MW																					20															20
Estimated cost of solar photovoltaic capacity																																				$ 48,900,000
Current output of solar photovoltaic capacity (in megawatts) | MW																					4															4
Expected output of solar photovoltaic capacity (in megawatts) | MW																					9															9
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Minimum [Member]
Rate Matters [Line Items]
Reasonable cost threshold																																	3.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Maximum [Member]
Rate Matters [Line Items]
Reasonable cost threshold																					3.00%															3.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Wind Energy [Member] | Minimum [Member]
Rate Matters [Line Items]
Required percentage of diversification																																	30.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Solar Energy [Member] | Minimum [Member]
Rate Matters [Line Items]
Required percentage of diversification																																	20.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Distributed Generation [Member] | Minimum [Member]
Rate Matters [Line Items]
Required percentage of diversification																																	3.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Other [Member] | Minimum [Member]
Rate Matters [Line Items]
Required percentage of diversification																																	5.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Required Percentage by 2011 [Member]
Rate Matters [Line Items]
Required percentage of renewable energy in portfolio to electric sales																																	10.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Required Percentage by 2015 [Member]
Rate Matters [Line Items]
Required percentage of renewable energy in portfolio to electric sales																																	15.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard [Member] | Required Percentage by 2020 [Member]
Rate Matters [Line Items]
Required percentage of renewable energy in portfolio to electric sales																																	20.00%
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard Supplemental Procurement [Member]
Rate Matters [Line Items]
Solar photovoltaic capacity (in megawatts) | MW																					1.5															1.5
Public Service Company of New Mexico [Member] | 2014 Wind generated Renewable Energy Credits [Member]
Rate Matters [Line Items]
Wind generation (in megawatt hours) | MWh																																			50,000
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard 2014 [Member]
Rate Matters [Line Items]
Solar photovoltaic capacity (in megawatts) | MW																																			23
Estimated cost of solar photovoltaic capacity																																			$ 46,500,000
Wind capacity, planned purchase agreement, term																																			20 years
Wind energy capacity (in megawatts) | MW																																			102
Cost of wind capacity in the first year, planned purchase agreement																																			$ 5,800,000
Public Service Company of New Mexico [Member] | 2015 Wind generated Renewable Energy Credits [Member]
Rate Matters [Line Items]
Wind generation (in megawatt hours) | MWh																																			120,000
Public Service Company of New Mexico [Member] | Renewable Portfolio Standard 2015 [Member]
Rate Matters [Line Items]
Solar photovoltaic capacity (in megawatts) | MW																																	40
Estimated cost of solar photovoltaic capacity																																	$ 79,300,000
Public Service Company of New Mexico [Member] | Renewable Energy Rider [Member]
Rate Matters [Line Items]
Revenue from renewable energy rider																																	$ 41,900,000		$ 31,900,000	$ 21,700,000
Public Service Company of New Mexico [Member] | Renewable Energy Rider [Member] | Maximum [Member]
Rate Matters [Line Items]
Rider condition of earned return on jurisdictional equity in 2013																																	10.50%		10.50%	10.50%
Annual revenue to be collected under 2015 rider rate																																	$ 42,400,000
Public Service Company of New Mexico [Member] | Energy Efficient and Load Management [Member] | Disincentives/Incentives Added [Member]
Rate Matters [Line Items]
Program costs related to energy efficiency																	$ 22,500,000
Authorization to recover an incentive equal to a percentage of annual program costs																7.60%
Annual incentive																																				$ 1,700,000
Public Service Company of New Mexico [Member] | 2014 Energy Efficiency and Load Management Program [Member] | Disincentives/Incentives Added [Member]
Rate Matters [Line Items]
Program costs related to energy efficiency									$ 25,800,000
Proposed energy efficiency incentive																																			$ 2,100,000
Anticipated future profit incentive 2015																																									$ 1,700,000
Anticipated future profit incentive 2016																																									$ 1,800,000
Public Service Company of New Mexico [Member] | FPPAC Continuation Application [Member]
Rate Matters [Line Items]
Retention percentage of sales margins											10.00%	10.00%
Under-collected balance write-off											$ 10,500,000										$ 10,500,000
Public Utilities, Under-collected balance to be collected										$ 63,500,000
Period of time to collect											18 months
Public Service Company of New Mexico [Member] | 2011 Integrated Resource Plan [Member]
Rate Matters [Line Items]
Planning period covered, IRP																																	20 years
Public Service Company of New Mexico [Member] | Transmission Rate Case [Member]
Rate Matters [Line Items]
Approved rate increase (decrease)																			$ 11,100,000
Approved return on equity																			12.25%
Increased annual transmission service revenue														$ 2,900,000
Public Service Company of New Mexico [Member] | Wholesale Electric Transmission Rate Case [Member] [Member]
Rate Matters [Line Items]
Approved rate increase (decrease)														$ 2,900,000																							$ 3,200,000
Approved return on equity																																					10.81%
Lease ownership in EIP													60.00%
Approved additional rate increase						$ 1,300,000
Public Service Company of New Mexico [Member] | Formula Transmission Rate Case [Member]
Rate Matters [Line Items]
Return on equity						10.00%
Public Service Company of New Mexico [Member] | Firm Requirements Wholesale Power Rate Case, Navopache [Member] [Member]
Rate Matters [Line Items]
Approved rate increase (decrease)															$ 5,300,000
Average monthly usage (in megawatts) | MW																																	54		55
Revenue for power sold under specific contract																																	$ 27,100,000		$ 28,400,000
Public Service Company of New Mexico [Member] | Firm Requirements Wholesale Power Rate Case, Navopache [Member] [Member] | Scenario, Forecast [Member]
Rate Matters [Line Items]
Public Utilities, Expected average monthly usage in megawatts | MW																														10
Public Service Company of New Mexico [Member] | Firm Requirements Wholesale Power Rate Case [Member]
Rate Matters [Line Items]
Contract extension															10 years
Public Service Company of New Mexico [Member] | Firm Requirements Wholesale Power Contract, Gallup [Member]
Rate Matters [Line Items]
Revenue for power sold under specific contract																										$ 6,100,000										$ 11,700,000
Public Service Company of New Mexico [Member] | City of Gallup, New Mexico Contract [Member]
Rate Matters [Line Items]
Gain on sale of substation																				$ 1,100,000
Texas-New Mexico Power Company [Member] | Advanced Meter System Deployment and Surcharge Request [Member]
Rate Matters [Line Items]
Approved deployment costs																		$ 113,400,000
Period of time to collect deployment costs through surcharge period																		12 years
Completion period of advanced meter deployment																		5 years
Non-standard metering service cost total to be borne by opt-out customers																																										$ 200,000
Non-standard metering ongoing expenses total to be borne by opt-out customers																																										500,000
Non-standard metering ongoing expenses monthly charge																																										$ 36.78
Presumed number of customers that will elect non-standard meter service (in customers) | customer																																										1,081
Cost and savings reconciliation filed with regulators, capital cost savings																																								$ 71,000,000
Cost and savings reconciliation filed with regulators, operations and maintenance savings																																								$ 18,000,000
Program costs incurred to date																																	$ 1,500,000
Texas-New Mexico Power Company [Member] | Advanced Meter System Deployment and Surcharge Request [Member] | Subsequent Event [Member]
Rate Matters [Line Items]
Current number of customers that have elected non-standard meter service (in customers) | customer																																							98
Texas-New Mexico Power Company [Member] | Advanced Meter System Deployment and Surcharge Request [Member] | Minimum [Member]
Rate Matters [Line Items]
Non-standard metering service cost initial fee range																																										$ 63.97
Texas-New Mexico Power Company [Member] | Advanced Meter System Deployment and Surcharge Request [Member] | Maximum [Member]
Rate Matters [Line Items]
Non-standard metering service cost initial fee range																																										$ 168.61
Texas-New Mexico Power Company [Member] | Energy Efficiency [Member]
Rate Matters [Line Items]
Aggregate Collection Amount																																		$ 5,600,000				$ 5,200,000
Performance Bonus																																		$ 700,000				$ 0
Texas-New Mexico Power Company [Member] | Energy Efficiency [Member] | Scenario, Forecast [Member]
Rate Matters [Line Items]
Aggregate Collection Amount																															$ 6,000,000	$ 5,700,000
Performance Bonus																															$ 700,000	$ 1,500,000
Texas-New Mexico Power Company [Member] | Transmission Cost of Service Rates [Member]
Rate Matters [Line Items]
Approved rate increase (decrease)																							$ 27,100,000	$ 25,200,000	$ 18,200,000		$ 18,100,000	$ 21,900,000	$ 26,400,000
Increased annual transmission service revenue																							$ 4,400,000	$ 4,200,000	$ 2,900,000		$ 2,800,000	$ 2,900,000	$ 2,500,000
Texas-New Mexico Power Company [Member] | Transmission Cost of Service Rates [Member] | Subsequent Event [Member]
Rate Matters [Line Items]
Requested rate increase (decrease)	$ 25,800,000
Requested increase in annual transmission service revenue	$ 4,300,000
Texas-New Mexico Power Company [Member] | Transmission Cost of Service Rates [Member] | Scenario, Forecast [Member]
Rate Matters [Line Items]
Approved rate increase (decrease)																						$ 7,000,000
Increased annual transmission service revenue																						$ 1,400,000