Commitments and Contingencies (Details) (USD $)	12 Months Ended					1 Months Ended	12 Months Ended		0 Months Ended			0 Months Ended	12 Months Ended			1 Months Ended		0 Months Ended	12 Months Ended													12 Months Ended											0 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 21, 2011 mw	Jan. 30, 2009	Jan. 31, 2008 Positive Outcome of 1992 Litigation [Member]	Dec. 31, 2010 Positive Outcome of 1992 Litigation [Member]	Oct. 21, 2009 Positive Outcome of 1992 Litigation [Member]	Jun. 18, 2010 Palo Verde Nuclear Generating Station [Member]	Dec. 21, 2011 San Juan Generating Station [Member]	Nov. 08, 2010 Four Corners [Member]	Jun. 18, 2010 Public Service Company of New Mexico [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member]	Dec. 31, 2009 Public Service Company of New Mexico [Member]	Jan. 31, 2011 Public Service Company of New Mexico [Member] Transmissions Issues [Member]	Dec. 31, 2009 Public Service Company of New Mexico [Member] Western United State Wholesale Power Market [Member]	Jun. 18, 2010 Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]		Dec. 31, 2010 Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2009 Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member] Nuclear Spent Fuel And Waste Disposal [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] San Juan Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Four Corners [Member] Clean Air Act related to Post-Combustion Controls [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Other Deferred Credits [Member] Palo Verde Nuclear Generating Station [Member] Nuclear Spent Fuel And Waste Disposal [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member] Other Deferred Credits [Member] Palo Verde Nuclear Generating Station [Member] Nuclear Spent Fuel And Waste Disposal [Member]	May 17, 2010 Public Service Company of New Mexico [Member] Minimum [Member] Citizen Suit Under the Clean Air Act [Member]	Jan. 06, 2010 Public Service Company of New Mexico [Member] Minimum [Member] San Juan Generating Station And Four Corners [Member] opp	May 17, 2010 Public Service Company of New Mexico [Member] Maximum [Member] Citizen Suit Under the Clean Air Act [Member]	Jan. 06, 2010 Public Service Company of New Mexico [Member] Maximum [Member] San Juan Generating Station And Four Corners [Member] opp	Dec. 31, 2011 Public Service Company of New Mexico [Member] Surface [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member] Surface [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2009 Public Service Company of New Mexico [Member] Surface [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Surface [Member] San Juan Generating Station [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Underground [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member] Underground [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Underground [Member] San Juan Generating Station [Member] Loss on Long-term Purchase Commitment [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Nuclear Plant [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Nuclear Plant [Member] Maximum [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Commercial Providers [Member] Nuclear Plant [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member] Industry Wide Retrospective Assessment Program [Member] Nuclear Plant [Member] Palo Verde Nuclear Generating Station [Member]	Jun. 18, 2010 Cost of Energy [Member] Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]	Jun. 18, 2010 Reduction of Utility Plant [Member] Public Service Company of New Mexico [Member] Palo Verde Nuclear Generating Station [Member]	Dec. 31, 2011 Installation Costs [Member] Public Service Company of New Mexico [Member] San Juan Generating Station [Member] Clean Air Act, SCR [Member]	Dec. 31, 2011 Installation Costs [Member] Public Service Company of New Mexico [Member] San Juan Generating Station [Member] Clean Air Act, SNCR [Member]	Dec. 31, 2011 Operating Costs [Member] Public Service Company of New Mexico [Member] San Juan Generating Station [Member] Clean Air Act, SCR [Member]	Feb. 27, 2012 Fuel and purchased power adjustment clause [Member] Filings with the New Mexico Public Regulation Commission [Member] Public Service Company of New Mexico [Member] San Juan Generating Station [Member]
Loss Contingencies [Line Items]
Payments to Acquire Investments to be Held in Decommissioning Trust Fund																			$ 2,600,000		$ 3,000,000	$ 3,000,000
Decommissioning Fund Investments, Fair Value																			168,900,000		156,900,000
Settlement of Legal Proceeding	0	0	31,969,000										0	0	31,969,000
Loss Contingency, Estimate of Possible Loss																							42,800,000		69,000,000			5,000,000		6,000,000					54,100,000			21,700,000								77,000,000
Reclamation and Mine Shutdown Costs Paid																																1,900,000	5,100,000	7,600,000
Mine Reclamation and Closing Liability, Noncurrent																										14,500,000	14,800,000					26,500,000	25,000,000			4,200,000	2,800,000
Final Reclamation, capped amount to be collected																																100,000,000
Preliminary estimate increased deferral related to mine fire incident																																																14,500,000
Minimum Megawatt Capacity from Coal and Oil-Fired Electric Generating Units under Jurisdiction of the Merucy and Air Toxics Standards				25
Mercury Removal Rate, Percentage										0.99
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners											48.00%
Loss Contingency, Range of Possible Loss, Minimum																																													750,000,000		21,300,000
Loss Contingency, Range of Possible Loss, Maximum																																													1,000,000,000		91,500,000
Jointly Owned Utility Plant, Proportionate Ownership Share																			10.20%	[1]				46.30%
Public Utilities, Government Standard Emission Limit (pounds per MMBTU, parts per million)																													0.060		0.070
Other current assets	33,397,000	96,110,000											26,776,000	46,635,000
Public Utilities, Liability Insurance Coverage																																								12,600,000,000	375,000,000	12,200,000,000
Public Utilities, Ownership Percentage in Nuclear Reactor																																							10.20%
Public Utilities, Maximum Potential Assessment Per Incident																																							36,000,000
Public Utilities, Annual Payment Limitation Related to Incident																																							5,400,000
Public Utilities, Aggregate Amount of All Risk Insurance																																							2,750,000,000
Public Utilities, Maximum Amount under Nuclear Electir Insurance Limited																																							5,800,000
Litigation Settlement, Gross						14,900,000			30,200,000			1,300,000				200,000	45,000,000	3,100,000																									2,100,000	1,000,000
Cost of Gas Recovery, Percent					100.00%
Litigation Settlement Amount, Revised by Appellate Court								9,700,000
Litigation settlement recorded in other income							1,200,000
Litigation Settlement Payment, Reassigned Receivables																	13,100,000
Litigation Settlement Payment, Cash on Hand																	$ 31,900,000

[1] (1) Includes interest in PVNGS Unit 3, interest in common facilities for all PVNGS units, and owned interests in PVNGS Units 1 and 2.