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Summary of the Business and Significant Accounting Policies (Details) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2013
Public Service Company of New Mexico [Member]
Dec. 31, 2012
Public Service Company of New Mexico [Member]
Dec. 31, 2011
Public Service Company of New Mexico [Member]
Dec. 31, 2013
Texas-New Mexico Power Company [Member]
Dec. 31, 2012
Texas-New Mexico Power Company [Member]
Dec. 31, 2011
Texas-New Mexico Power Company [Member]
Jan. 04, 2012
Optim Energy [Member]
Dec. 31, 2012
Optim Energy [Member]
Sep. 23, 2011
Optim Energy [Member]
Sep. 22, 2011
Optim Energy [Member]
Dec. 31, 2013
Palo Verde Nuclear Generating Station [Member]
Public Service Company of New Mexico [Member]
Operating_Leases
Dec. 31, 1986
Palo Verde Nuclear Generating Station [Member]
Public Service Company of New Mexico [Member]
Operating_Leases
Dec. 31, 2004
EIP Transmission Line [Member]
Public Service Company of New Mexico [Member]
Dec. 31, 2003
EIP Transmission Line [Member]
Public Service Company of New Mexico [Member]
Dec. 31, 1985
EIP Transmission Line [Member]
Public Service Company of New Mexico [Member]
Operating_Leases
Dec. 31, 2013
10.3% Lessor Notes [Member]
Public Service Company of New Mexico [Member]
Dec. 31, 2013
10.15% Lessor Notes [Member]
Public Service Company of New Mexico [Member]
Dec. 31, 2013
10.25% EIP Lessor Note Maturing in 2012 [Member]
EIP Transmission Line [Member]
Public Service Company of New Mexico [Member]
Accounting Policies Disclosures [Line Items]                                          
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset $ 19,900,000     $ 11,100,000     $ 6,800,000                            
Equity method investment,ownership percentage (as a percent)                         50.00%                
Allowance for funds used during construction, capitalized interest       3,300,000 3,500,000 1,500,000 400,000 700,000 600,000                        
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity       4,400,000 3,800,000 0 0 600,000 600,000                        
Debt, weighted average interest rate (as a percent) 6.90% 6.60% 6.60%                                    
Interest costs incurred, capitalized 1,500,000 1,200,000 500,000 1,100,000 800,000 200,000                              
Number of operating leases (in ones)                           8 11     2      
Notes receivable, stated percentage rate (as a percent)                                     10.30% 10.15% 10.25%
Ownership percentage acquired (as a percent)                               40.00% 60.00%        
Other investments 1,835,000 5,599,000   445,000 494,000   245,000 281,000                          
Impairment losses on securities held in the NDT       3,500,000 4,800,000 12,500,000                              
Cost method investment, ownership percentage (as a percent)                       1.00%                  
Ownership percentage, sold (as a percent)                   1.00%                      
Cost Method Investments                   0                      
Equity Method Investments                     $ 0