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Regulatory and Rate Matters - Hazard Sharing Agreement (Details) - Public Service Company of New Mexico - Tri-State GWh in Millions, $ in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Jun. 01, 2017 | Jun. 01, 2016 MW | Dec. 31, 2017 USD ($) GWh | Dec. 31, 2016 USD ($) GWh
Public Utilities, General Disclosures [Line Items] |  |  |  |
Hazard sharing agreement | 5 years | 1 year |  |
Agreement to sell the other party capacity and energy (in mw) | MW |  | 100 |  |
Number of hours sold (in GWh) | GWh |  |  | 827.1 | 482.3
Hours sold (in dollars) | $ |  |  | $ 23.6 | $ 12.8
Number of hours purchased (in GWh) | GWh |  |  | 849.0 | 484.6
Hours purchased (in dollars) | $ |  |  | $ 24.2 | $ 12.9

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