Regulatory and Rate Matters (Details) (USD $) In Millions, unless otherwise specified			1 Months Ended	3 Months Ended															3 Months Ended			0 Months Ended	3 Months Ended				0 Months Ended	3 Months Ended				3 Months Ended			12 Months Ended	1 Months Ended	0 Months Ended					0 Months Ended			1 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended	1 Months Ended
	Mar. 31, 2013 Public Service Company of New Mexico [Member] Emergency FPPAC [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] La Luz Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] MW	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Minimum [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Maximum [Member]	Dec. 31, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Wind Energy [Member] Minimum [Member]	Sep. 30, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Wind Energy [Member] Minimum [Member]	Dec. 31, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Solar Energy [Member] Minimum [Member]	Sep. 30, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Solar Energy [Member] Minimum [Member]	Dec. 31, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Renewable Technologies [Member] Minimum [Member]	Sep. 30, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Renewable Technologies [Member] Minimum [Member]	Dec. 31, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Distributed Generation [Member] Minimum [Member]	Sep. 30, 2012 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Distributed Generation [Member] Minimum [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Required Percentage by 2011 [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Required Percentage by 2015 [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Required Percentage by 2015 [Member] Distributed Generation [Member] Minimum [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard [Member] Required Percentage by 2020 [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard Supplemental Procurement [Member] MW	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard Supplemental Procurement Reduction [Member] Minimum [Member] MW	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Portfolio Standard Supplemental Procurement Reduction [Member] Maximum [Member] MW	Aug. 20, 2011 Public Service Company of New Mexico [Member] NMPRC Rulemaking on Disincentives to Energy Efficiency Programs [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] NMPRC Rulemaking on Disincentives to Energy Efficiency Programs [Member]	Nov. 29, 2010 Public Service Company of New Mexico [Member] NMPRC Rulemaking on Disincentives to Energy Efficiency Programs [Member]	May 03, 2010 Public Service Company of New Mexico [Member] NMPRC Rulemaking on Disincentives to Energy Efficiency Programs [Member] Per KWh [Member] Maximum [Member]	May 03, 2010 Public Service Company of New Mexico [Member] NMPRC Rulemaking on Disincentives to Energy Efficiency Programs [Member] Per kilowatt [Member]	Oct. 05, 2012 Public Service Company of New Mexico [Member] 2010 Energy Efficiency Application [Member] Disincentives / Incentives Adder [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] 2010 Energy Efficiency Application [Member] Disincentives / Incentives Adder [Member]	Aug. 11, 2011 Public Service Company of New Mexico [Member] 2010 Energy Efficiency Application [Member] Disincentives / Incentives Adder [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] 2010 Energy Efficiency Application [Member] Per KWh [Member] Amended [Member] Minimum [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] 2010 Energy Efficiency Application [Member] Per kilowatt [Member] Amended [Member] Minimum [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] 2010 Electric Rate Case [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Energy Rider [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Renewable Energy Rider [Member] Maximum [Member]	Dec. 31, 2012 Public Service Company of New Mexico [Member] Renewable Energy Rider [Member] Maximum [Member]	Jul. 31, 2011 Public Service Company of New Mexico [Member] Integrated Resource Plan, 2011 [Member] Protests_Filed	Jul. 03, 2012 Public Service Company of New Mexico [Member] Transmission Rate Case [Member]	Oct. 27, 2010 Public Service Company of New Mexico [Member] Transmission Rate Case [Member]	May 01, 2013 Public Service Company of New Mexico [Member] Formula Transmission Rate Case [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] Formula Transmission Rate Case [Member]	Jan. 02, 2013 Public Service Company of New Mexico [Member] Formula Transmission Rate Case [Member]	Dec. 06, 2012 Public Service Company of New Mexico [Member] Firm Requirements Wholesale Power Rate Case [Member]	Sep. 15, 2011 Public Service Company of New Mexico [Member] Firm Requirements Wholesale Power Rate Case [Member]	Mar. 31, 2013 Public Service Company of New Mexico [Member] City of Gallup, New Mexico Contract [Member]	Jul. 31, 2011 Texas-New Mexico Power Company [Member] Advanced Meter System Deployment and Surcharge Request [Member]	Aug. 28, 2012 Texas-New Mexico Power Company [Member] Energy Efficiency [Member]	Mar. 31, 2013 Texas-New Mexico Power Company [Member] Energy Efficiency [Member]	Aug. 23, 2012 Texas-New Mexico Power Company [Member] Transmission Cost of Service Rates [Member]	Mar. 31, 2013 Subsequent Event [Member] Public Service Company of New Mexico [Member] 2010 Electric Rate Case [Member]	Jan. 31, 2013 Subsequent Event [Member] Texas-New Mexico Power Company [Member] Transmission Rate Filings [Member]	Mar. 31, 2013 Delta [Member] Public Service Company of New Mexico [Member] Applications for Approvals to Purchase Delta [Member] MW
Rate Matters [Line Items]
Public Utilities, Required Percentage of Renewable Energy in Portfolio to Electric Sales															10.00%	15.00%		20.00%
Public Utilities, Required Percentage of Diversification							30.00%	20.00%	20.00%	20.00%	5.00%	10.00%	1.50%	1.50%			3.00%
Public Utilities, Reasonable Cost Threshold					2.00%	3.00%
Public Utilities, Annual Incremental Increase in Reasonable Cost Threshold				0.25%
Public Utilites, Additional Renewable Procurements Spending Required by NMPRC			$ 0.9
Public Utilities, Number of Mega Watts of Solar PV Capacity				20															2	1.5	2
Public Utilities, Estimated Cost of Mega Watts of Solar PV Capacity				45.5															4.5
Public Utilities, Program Costs Related To Energy Efficiency																											22.5
Public Utilities, Proposed Profit Incentive Adder Revenues Related To Energy Efficiency Program																											4.2	2.9
Public Utilities, Rate Adder Allowed																									0.01	10				0.002	4
Public Utilities, Rate Rider Recovered																						2.6
Public Utilities, Regulatory Costs Approved																								4.2																	2.9
Percentage ownership of EIP transmission line																																								60.00%
Public Utilities, Eliminated Recovery of Adder Revenue																													1.3
Public Utilities, Rate Rider Net Over-Recovery																							0.2
Public Utilities, Rate Rider Program Costs Over-Recovery																							1.0
Public Utilities, Rate Rider Incentives Under-Recovery																							0.8
Public Utilities, Rate Rider Estimated Incentives Under-Recovery																							0.5
Public Utilities, Regulatory Costs to be Collected																																38.8																	36.2
Public Utilities, Additional Revenue To be Collected in 2012																																			18.0
Public Utilities, Additional Revenue To be Collected in 2013																																		24.6
Public Utilities, Rider Condition of Earned Return on Jurisdictional Equity in 2013																																		10.50%
Public Utilities, Proposed percentage increase to be implemented in May 2013																																	3.37%
Public Utilities, Approved Rider Rate For 2012																																	0.0022335
Public Utilities, Approved Rider Rate For 2013																																	0.0028371
Public Utilities, Order Disapproved Recovery of Costs As Regulatory Agency Had Not Acted on Specific Procurements Proposed																																	0.9
Public Utilities, Planning Period Covered of IRP																																				20 years
Public Utilities, Number of protests that were filed to IRP requesting rejection of the plan																																				2
Amount of Regulatory Costs Not yet Approved	8.0																																					11.1	1.3	3.2			8.7
Public Utilites, Number of Mega Watts Natural Gas Peaking Units to be Purchased																																																			132
Estimated Installation Capital Costs		63.2
Public Utilities, Return on Equity																																						0.1225		0.1081
Public Utilities, Regulatory Rate Increase																																											0.398
Public Utilities, Collection of Deployment Costs Through Surcharge Period																																													12 years
Public Utilities, Completion Period of Advanced Meter Deployment																																													5 years
Public Utilities, Increase Annual Transmission Service Revenue																																					2.9											2.5
Public Utilities, Requested Increase in Total Base to Reflect Changes in Invested Capital																																																26.4
Public Utilities, Additional Revenue from Proposed Rates																																																		21.9
Public Utilities, Total Revenue Requirement Increase																																										5.3								2.9
Public Utilities, Contract Extension																																										10 years
Public Utilities, Estimated Increase in Revenue over amendment term																																												3.1
Public Utilities, Approved Deployment Costs																																													113.3
Public Utilities, Approved Program Implementation Costs																																														4.8
Public Utilities, Approved Program Implementation Costs, Bonus																																														0.4
Public Utilities, Unapproved 2014 Program Implementation Costs																																															4.7
Public Utilities, Unapproved 2012 Program Implementation Costs, Bonus																																															$ 0.7