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Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) - Palo Verde Nuclear Generating Station [Member] - Public Service Company of New Mexico [Member] - USD ($) |  | 3 Months Ended |  |
--- | --- | --- | --- | ---
May 16, 2014 | Mar. 31, 2015 | Sep. 30, 2016 | Dec. 31, 2015
Department of energy, spent nuclear fuel removal July 2011 - June 2014 [Member] |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
PNM's share of third party settlement claim |  | $ 4,300,000 |  |
Litigation settlement, portion credited to customers |  | $ 3,100,000 |  |
Nuclear spent fuel and waste disposal [Member] |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Estimate of possible loss |  |  | $ 58,000,000 |
Revised annual fee, nuclear waste disposal | $ 0 |  |  |
Nuclear spent fuel and waste disposal [Member] | Other Deferred Credits [Member] |  |  |  |
Public Utilities, Commitments And Contingencies [Line Items] |  |  |  |
Loss contingency accrual |  |  | $ 12,000,000 | $ 12,200,000

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