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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 |

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