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Asset Retirement Obligations (Details) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Liability Beginning Balance $ 79,233,000 $ 76,637,000 $ 70,963,000 [1]
Liabilities incurred 0 60,000 532,000
Liabilities settled (25,000) (4,000) (603,000)
Accretion expense 6,685,000 6,114,000 6,019,000
Revisions to estimated cash flows   (3,574,000) (274,000)
Liability Ending Balance 85,893,000 79,233,000 76,637,000
Asset Retirement Obligation 85,893,000 79,233,000 76,637,000
Public Service Company of New Mexico [Member]
      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Liability Beginning Balance 78,425,000 75,888,000 70,099,000 [1]
Liabilities incurred 0 60,000 531,000
Liabilities settled 0 0 (413,000)
Accretion expense 6,617,000 6,051,000 5,945,000
Revisions to estimated cash flows   (3,574,000) (274,000)
Liability Ending Balance 85,042,000 78,425,000 75,888,000
Asset Retirement Obligation 85,042,000 78,425,000 75,888,000
Texas-New Mexico Power Company [Member]
      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Liability Beginning Balance 699,000 648,000 771,000 [1]
Liabilities incurred 0 0 0
Liabilities settled (25,000) (4,000) (190,000)
Accretion expense 58,000 55,000 67,000
Revisions to estimated cash flows   0 0
Liability Ending Balance 732,000 699,000 648,000
Asset Retirement Obligation 732,000 699,000 648,000
Palo Verde Nuclear Generating Station [Member] | Public Service Company of New Mexico [Member]
      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Nuclear Decommissioning License Extension Term   20 years  
Asset Retirement Obligation, Period Increase (Decrease)   $ (4,200,000)  
[1] Based on studies to estimate amount and timing of future ARO expenditures. PNM has an ARO for PVNGS that includes the obligations for nuclear decommissioning of that facility. In 2011, a new decommissioning study for PVNGS reflects updated cash flow estimates and the 20-year license extension, which extends the commencement of decommissioning to 2045. The new study resulted in a $4.2 million decrease to the ARO.