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Income Taxes (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2015
Income Tax Contingency [Line Items] |  |  |
New Mexico Corporate tax rate, 2014 | 7.60% |  |
New Mexico Corporate tax rate, effective by 2018 |  |  | 5.90%
Increase (decrease) in regulatory liability | $ (7.1) | $ (2.0) |
Impairment of state net operating loss carryforward | 0.0 | 1.0 |
Public Service Company of New Mexico [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Increase (decrease) in deferred tax assets as a result of tax rate changes | (0.7) | 0.7 |
Increase (decrease) in tax expense due to tax rate change | 0.8 | (0.5) |
Impairment of state net operating loss carryforward |  | 0.7 |
Texas-New Mexico Power Company [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Impairment of state net operating loss carryforward |  | 0.0 |
Corporate and Other [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Increase (decrease) in tax expense due to tax rate change | $ (0.1) | (0.2) |
Impairment of state net operating loss carryforward |  | $ 0.3 |

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