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Summary of the Business and Significant Accounting Policies - Narrative (Details) | 12 Months Ended |
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Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 1986 Operating_Leases
Accounting Policies Disclosures [Line Items] |  |  |  |
Allowance for equity funds used during construction | $ 10,430,000 | $ 5,563,000 | $ 4,382,000 |
Weighted average borrowing rate | 6.60% | 6.60% | 6.90% |
Interest costs incurred, capitalized | $ 1,500,000 | $ 1,600,000 | $ 1,500,000 |
Public Service Company of New Mexico [Member] |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |
Allowance for funds used during construction, capitalized interest | 7,800,000 | 4,200,000 | 3,300,000 |
Allowance for equity funds used during construction | 10,430,000 | 5,563,000 | 4,382,000 |
Interest costs incurred, capitalized | 800,000 | 1,100,000 | 1,100,000 |
Impairment losses on securities held in the NDT | $ 10,400,000 | 4,800,000 | 3,500,000 |
Public Service Company of New Mexico [Member] | 10.3% Lessor Notes [Member] |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |
Notes receivable, stated percentage rate | 10.30% |  |  |
Public Service Company of New Mexico [Member] | 10.15% Lessor Notes [Member] |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |
Notes receivable, stated percentage rate | 10.15% |  |  |
Public Service Company of New Mexico [Member] | Palo Verde Nuclear Generating Station [Member] |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |
Number of operating leases | Operating_Leases |  |  |  | 11
Texas-New Mexico Power Company [Member] |  |  |  |
Accounting Policies Disclosures [Line Items] |  |  |  |
Allowance for funds used during construction, capitalized interest | $ 500,000 | 500,000 | 400,000 |
Allowance for equity funds used during construction | 0 | 0 | 0 |
Interest costs incurred, capitalized | $ 100,000 | $ 100,000 | $ 0 |

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