Commitments and Contingencies (Other Commitments and Contingencies) (Details) (USD $)									3 Months Ended							3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Public Service Company of New Mexico [Member]	Dec. 31, 2012 Public Service Company of New Mexico [Member]	Oct. 31, 2012 Public Service Company of New Mexico [Member]	Mar. 31, 2013 San Juan Generating Station [Member] Public Service Company of New Mexico [Member] Coal Supply [Member]	Dec. 31, 2012 San Juan Generating Station [Member] Public Service Company of New Mexico [Member] Coal Supply [Member]	Mar. 31, 2013 Surface [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 TGP Granada, LLC and its affiliate Complaint [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 TGP Granada, LLC and its affiliate Complaint [Member] Tortoise Capital Resources Corporation [Member]	Mar. 31, 2013 Fuel and Purchased Power Adjustment Clause [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Nuclear Plant [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Nuclear Plant [Member] Maximum [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Nuclear Plant [Member] Commercial Providers [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Nuclear Plant [Member] Industry Wide Retrospective Assessment Program [Member] Palo Verde Nuclear Generating Station [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Loss on Long-term Purchase Commitment [Member] Surface [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2012 Loss on Long-term Purchase Commitment [Member] Surface [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Loss on Long-term Purchase Commitment [Member] Surface [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Loss on Long-term Purchase Commitment [Member] Underground [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2012 Loss on Long-term Purchase Commitment [Member] Underground [Member] Public Service Company of New Mexico [Member]	Mar. 31, 2013 Loss on Long-term Purchase Commitment [Member] Underground [Member] San Juan Generating Station [Member] Public Service Company of New Mexico [Member]
Public Utilities, Commitments and Contingencies [Line Items]
Other current assets	$ 40,414,000	$ 31,490,000	$ 37,052,000	$ 27,457,000		$ 14,100,000	$ 9,900,000
Final Reclamation, capped amount to be collected																100,000,000
Preliminary estimate increased deferral related to mine fire incident											21,600,000
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, Sublimit Amount under Nuclear Electric Insurance Limited												1,500,000,000
Public Utilities, Maximum Amount under Nuclear Electir Insurance Limited												4,300,000
Public Utilities, Lease ownership percentage in EIP									60.00%	40.00%
Public Utilities, Option to Purchase Leased Capacity At Fair Value					7,700,000
Loss Contingency, Estimate of Possible Loss																		59,900,000			19,700,000
Loss Contingency Accrual, at Carrying Value																25,900,000	26,800,000		4,300,000	4,200,000
Regulatory Assets								$ 100,000,000