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Regulatory and Rate Matters - Integrated Resource Plan, Four Corners Right of First Refusal and Application for Certificate (Details) - Public Service Company of New Mexico [Member] $ in Millions | 1 Months Ended | 3 Months Ended | 4 Months Ended |
--- | --- | --- | --- | ---
Jul. 31, 2011 | Sep. 30, 2015 USD ($) MW | Jun. 17, 2015 | Feb. 17, 2015
Four Corners [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Jointly owned utility plant proportionate ownership share, other entities |  |  |  | 7.00%
Period of time to file a waiver of rights of first refusal |  |  | 120 days |
San Juan Generating Station Units 2 and 3 [Member] | Clean Air Act, SNCR [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, newly identified replacement gas-fired generation (in megawatts) | MW |  | 187 |  |
Public utilities, cost of replacement gas-generation |  | $ 133.2 |  |
Integrated Resource Plan, 2011 [Member] |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Public utilities, frequency of IRP filings |  | 3 years |  |
Public utilities, planning period covered of IRP | 20 years |  |  |

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