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Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
 1 Months Ended 3 Months Ended
May 31, 2013
Sep. 30, 2013
Jun. 30, 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     1.2  
Additional Income Tax Expense, Impairment of NM Wind Credits     2.4  
Federal Tax Refund 96.2      
Public Service Company of New Mexico [Member]
        
Income Tax Contingency [Line Items]        
Federal Tax Refund 77.4      
PNMR to PNM [Member]
        
Income Tax Contingency [Line Items]        
Federal Income Tax Refund Transferred to Related Party   $ 45.0