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Regulatory and Rate Matters (Details) (USD $)	12 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended		0 Months Ended		12 Months Ended	0 Months Ended	1 Months Ended		6 Months Ended				12 Months Ended	6 Months Ended		4 Months Ended
Regulatory and Rate Matters (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2011	Dec. 31, 2014 MW	Dec. 31, 2013	Dec. 31, 2012	Oct. 05, 2012	Oct. 06, 2014	Dec. 31, 2011	Dec. 06, 2012	Jul. 31, 2011	Jun. 30, 2012	Sep. 07, 2014	Mar. 12, 2014	Sep. 16, 2013	Mar. 19, 2013	Dec. 31, 2015	Sep. 15, 2015	Mar. 15, 2015	Jun. 17, 2015	Jan. 31, 2012	Feb. 20, 2015 customer	Feb. 17, 2015
Public Service Company of New Mexico [Member] \| 2014 Electric Rate Case [Member]
Rate Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 107,400,000
Public Utilities, Requested Return on Equity, Percentage	10.50%
Public Utilities, Average customer bill increase percentage	7.69%
Public Utilities, Percentage of requested rate increase pertaining to infrastructure investments	92.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member]
Rate Matters [Line Items]
Public Utilites, Additional Renewable Procurements Spending Required by NMPRC		900,000
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity	20		20
Public Utilities, Estimated Cost of Mega Watts of Solar Photovoltaic Capacity			45,500,000
Public Utilities, Final Cost of Solar Photovoltaic Capacity				48,900,000
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity, Current Output	4		4
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity, Expected Output	10		10
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Minimum [Member]
Rate Matters [Line Items]
Public Utilities, Reasonable Cost Threshold	3.00%		3.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Maximum [Member]
Rate Matters [Line Items]
Public Utilities, 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]
Public Utilities, Required Percentage of Diversification	30.00%		30.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Solar Energy [Member] \| Minimum [Member]
Rate Matters [Line Items]
Public Utilities, Required Percentage of Diversification	20.00%		20.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Renewable Technologies [Member] \| Minimum [Member]
Rate Matters [Line Items]
Public Utilities, Required Percentage of Diversification	5.00%		5.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Distributed Generation [Member] \| Minimum [Member]
Rate Matters [Line Items]
Public Utilities, Required Percentage of Diversification	1.50%		1.50%
Public Utilities, Future Required Percentage of Diversification	3.00%		3.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Required Percentage by 2011 [Member]
Rate Matters [Line Items]
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales	10.00%		10.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Required Percentage by 2015 [Member]
Rate Matters [Line Items]
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales	15.00%		15.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard [Member] \| Required Percentage by 2020 [Member]
Rate Matters [Line Items]
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales	20.00%		20.00%
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard Supplemental Procurement [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity	2		2
Public Utilities, Estimated Cost of Mega Watts of Solar Photovoltaic Capacity			4,500,000
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard Supplemental Procurement Reduction [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity	1.5		1.5
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard Supplemental Procurement Reduction [Member] \| Maximum [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity	2		2
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard 2014 [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity	23		23
Public Utilities, Estimated Cost of Mega Watts of Solar Photovoltaic Capacity	46,700,000
Public Utilities, Wind Capacity Planned Purchase Agreement Term	20 years
Public Utilities, Number of Mega Watts of Wind Energy Capacity	102
Public Utilities, First Year Cost of Wind Capacity Planned Purchase Agreement	5,800,000.0
Public Service Company of New Mexico [Member] \| Renewable Portfolio Standard 2015 [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watts of Solar Photovoltaic Capacity	40		40
Public Utilities, Estimated Cost of Mega Watts of Solar Photovoltaic Capacity	79,300,000
Public Utilities, Approved cost per MWh for additional necessary procurements to comply with RPS	4.25
Public Utilities, Approved Revised cost per MWh for additional necessary procurements to comply with RPS	3.00
Public Utilities, Number of MegaWatt Hours of renewable resources	44,000
Public Utilities, Actual cost per MWh for additional necessary procurements to comply with RPS	1.75
Public Service Company of New Mexico [Member] \| 2014 Wind generated Renewable Energy Credits [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watt Hours of Wind Generation	50,000
Public Service Company of New Mexico [Member] \| 2015 Wind generated Renewable Energy Credits [Member]
Rate Matters [Line Items]
Public Utilities, Number of Mega Watt Hours of Wind Generation	120,000
Public Service Company of New Mexico [Member] \| Renewable Energy Rider [Member]
Rate Matters [Line Items]
Public Utilities, Revenue from Renewable energy rider	34,300,000			23,700,000	6,400,000
Public Service Company of New Mexico [Member] \| Renewable Energy Rider [Member] \| Maximum [Member]
Rate Matters [Line Items]
Public Utilities, Rider Condition of Earned Return on Jurisdictional Equity in 2013	10.50%
Public Utilities, Annual Revenue To be Collected Under 2015 Rider Rate	44,700,000		44,700,000
Public Service Company of New Mexico [Member] \| Energy Efficient and Load Management [Member] \| Disincentives / Incentives Adder [Member]
Rate Matters [Line Items]
Public Utilities, Program Costs Related To Energy Efficiency						22,500,000
Public Utilities, Approved Profit Incentive Adder Revenues Related To Energy Efficiency Program, Percentage of Program Costs	7.60%
Public Utilities, Approved Profit Incentive Adder Revenues Related To Energy Efficiency Program				1,700,000
Public Utilities, Energy Efficiency Incentive adder collected				1,300,000
Public Service Company of New Mexico [Member] \| FPPAC Continuation Application [Member]
Rate Matters [Line Items]
Public Utilities, Retention Percentage of Sales Margins	10.00%
Public Utilities, Under-collected balance write-off				10,500,000
Public Utilities, Under-recovery expected to be collected	63,500,000		63,500,000
Public Service Company of New Mexico [Member] \| FPPAC Continuation Application [Member] \| Maximum [Member]
Rate Matters [Line Items]
Public Utilities, Fuel Costs to be Collected				36,200,000	38,800,000
Public Service Company of New Mexico [Member] \| 2014 Energy Efficiency and Load Management Program [Member] \| Disincentives / Incentives Adder [Member]
Rate Matters [Line Items]
Public Utilities, Program Costs Related To Energy Efficiency							25,800,000
Public Utilities, Proposed Profit Incentive Adder Revenues Related To Energy Efficiency Program	2,100,000
Public Utilities, Anticipated future profit incentive 2015	1,700,000		1,700,000
Public Utilities, Anticipated future profit incentive 2016	1,800,000		1,800,000
Public Service Company of New Mexico [Member] \| Nmprc Rulemaking on Disincentives to Energy Efficiency Programs [Member]
Rate Matters [Line Items]
Public Utilities, Rate Rider Net Over-Recovery				200,000
Public Utilities, Rate Rider Program Costs Over-Recovery				1,000,000
Public Utilities, Rate Rider Incentives Under-Recovery				800,000
Public Utilities, Rate Rider Estimated Incentives Under-Recovery				500,000
Public Service Company of New Mexico [Member] \| 2011 Integrated Resource Plan [Member]
Rate Matters [Line Items]
Public Utilities, Planning Period Covered of IRP	20 years
Public Service Company of New Mexico [Member] \| Transmission Rate Case [Member]
Rate Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount								11,100,000
Public Utilities, Approved Return on Equity, Percentage								12.25%
Public Utilities, Increase 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]
Public Utilities, Approved Rate Increase (Decrease), Amount				2,900,000	3,200,000
Public Utilities, Approved Return on Equity, Percentage				10.81%
Public Utilities, Lease ownership percentage in EIP	60.00%
Public Utilities, Approved additional rate increase, Amount	500,000			1,300,000
Public Service Company of New Mexico [Member] \| Firm Requirements Wholesale Power Rate Case, Navopache [Member] [Member]
Rate Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount								8,700,000
Public Utilities, Approved Rate Increase (Decrease), Amount									5,300,000
Public Utilities, Regulatory Rate Increase								39.80%
Public Service Company of New Mexico [Member] \| Firm Requirements Wholesale Power Rate Case [Member]
Rate Matters [Line Items]
Public Utilities, Contract Extension									10 years
Public Service Company of New Mexico [Member] \| Firm Requirements Wholesale Power Contract, Gallup [Member]
Rate Matters [Line Items]
Public Utilities, Revenue For Power Sold Under Specific Contract	6,100,000			11,700,000
Texas-New Mexico Power Company [Member] \| Advanced Meter System Deployment and Surcharge Request [Member]
Rate Matters [Line Items]
Public Utilities, Approved Deployment Costs										113,400,000
Public Utilities, Collection of Deployment Costs Through Surcharge Period										12 years
Public Utilities, Completion Period of Advanced Meter Deployment										5 years
Public Utilities, Non-standard metering service cost total to be borne by opt-out customers				200,000
Public Utilities, Non-standard metering ongoing expenses total to be borne by opt-out customers				500,000
Public Utilities, Non-standard metering ongoing expenses monthly charge				38.99
Public Utilities, Non-standard metering service cost total to be borne by opt-out customers	200,000		200,000
Public Utilities, Non-standard metering ongoing expenses total to be borne by opt-out customers	500,000		500,000
Public Utilities, Non-standard metering ongoing expenses monthly charge	36.78		36.78
Presumed number of customers that will elect non-standard meter service	1,081		1,081
Texas-New Mexico Power Company [Member] \| Advanced Meter System Deployment and Surcharge Request [Member] \| Minimum [Member]
Rate Matters [Line Items]
Public Utilities, Non-standard metering service cost, Proposed initial fee range				142.84
Public Utilities, Non-standard metering service cost initial fee range	63.97		63.97
Texas-New Mexico Power Company [Member] \| Advanced Meter System Deployment and Surcharge Request [Member] \| Maximum [Member]
Rate Matters [Line Items]
Public Utilities, Non-standard metering service cost, Proposed initial fee range				247.48
Public Utilities, Non-standard metering service cost initial fee range	168.61		168.61
Texas-New Mexico Power Company [Member] \| Ercot Transmission Rates [Member]
Rate Matters [Line Items]
Public Utilities, Eliminated Recovery of Adder Revenue																				1,600,000
Public Utilities, Additional Transmission Costs Requested											3,200,000
Texas-New Mexico Power Company [Member] \| Ercot Transmission Rates [Member] \| PUCT staff agreed to interim rate relief that will permit TNMP to add uncontested costs to its existing TCRF [Member]
Rate Matters [Line Items]
Public Utilities, Approved Additional Transmission Costs				1,600,000
Texas-New Mexico Power Company [Member] \| Energy Efficiency [Member]
Rate Matters [Line Items]
Public Utilities, Approved Program Implementation Costs	5,600,000			5,200,000	3,400,000
Public Utilities, Approved Program Implementation Costs, Bonus	1,500,000				300,000
Public Utilities, Unapproved 2015 Program Implementation Costs, Bonus	700,000		700,000	1,500,000
Public Utilities, Unapproved 2015 Program Implementation Costs	5,700,000		5,700,000
Texas-New Mexico Power Company [Member] \| Transmission Cost of Service Rates [Member]
Rate Matters [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount												18,200,000	18,100,000	21,900,000	26,400,000
Public Utilities, Increase Annual Transmission Service Revenue												2,900,000	2,800,000	2,900,000	2,500,000
Texas-New Mexico Power Company [Member] \| Subsequent Event [Member] \| Advanced Meter System Deployment and Surcharge Request [Member]
Rate Matters [Line Items]
Current number of customers that have elected non-standard meter service																					89
Texas-New Mexico Power Company [Member] \| Subsequent Event [Member] \| Energy Efficiency [Member]
Rate Matters [Line Items]
Public Utilities, Approved Program Implementation Costs																5,700,000
Texas-New Mexico Power Company [Member] \| Subsequent Event [Member] \| Transmission Cost of Service Rates [Member]
Rate Matters [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount																	27,100,000
Public Utilities, Approved Rate Increase (Decrease), Amount																		25,200,000
Public Utilities, Increase Annual Transmission Service Revenue																		4,200,000
Public Utilities, Requested Increase Annual Transmission Service Revenue																	$ 4,400,000
Four Corners [Member] \| Public Service Company of New Mexico [Member] \| Subsequent Event [Member]
Rate Matters [Line Items]
Jointly Owned Utility Plant Proportionate Ownership Share, Other Entities																						7.00%
Period of time to file a waiver of rights of first refusal																			120 days