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Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2014
Jun. 30, 2013
Dec. 31, 2013
Mar. 31, 2013
Income Tax Contingency [Line Items]        
Deferred Tax Assets, Operating Loss Carryforwards, State and Local, Decrease       $ 1.5
New Mexico Corporate tax rate, current 7.60%      
New Mexico Corporate tax rate, 2014 5.90%      
Increase in regulatory liabilities due to change in state corporate tax rate 23.9      
Increase in income tax expense due to change in state corporate tax rate 0.2 1.2    
Decrease in regulatory liabilities due to change in state corporate tax rate 4.6      
Additional Income Tax Expense, Impairment of NM Wind Credits   2.4    
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset     19.9  
Public Service Company of New Mexico [Member]
        
Income Tax Contingency [Line Items]        
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset     11.2  
Texas-New Mexico Power Company [Member]
        
Income Tax Contingency [Line Items]        
New Accounting Pronouncements Not Yet Adopted, Effect on Deferred Tax Asset     $ 6.8