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Regulatory and Rate Matters - TNMP Narrative (Details) - Texas-New Mexico Power Company [Member] advanced_meter in Thousands |  | 1 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jan. 20, 2017 USD ($) | Jul. 31, 2011 USD ($) | Dec. 31, 2016 USD ($) advanced_meter | Feb. 21, 2017 customer | Oct. 02, 2015 USD ($) | Jun. 20, 2014 USD ($) | Aug. 15, 2013 USD ($) customer
Advanced Meter System Deployment and Surcharge Request [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Approved deployment costs |  | $ 113,400,000 |  |  |  |  |
Period of time to collect deployment costs through surcharge period |  | 12 years |  |  |  |  |
Number of advanced meters installed | advanced_meter |  |  | 242 |  |  |  |
Non-standard metering service cost total to be borne by opt-out customers |  |  |  |  |  |  | $ 200,000
Non-standard metering ongoing annual expenses to be borne by opt-out customers |  |  |  |  |  |  | $ 500,000
Non-standard metering ongoing expenses monthly charge |  |  |  |  |  | $ 36.78 |
Presumed number of customers that will elect non-standard meter service (in customers) | customer |  |  |  |  |  |  | 1,081
Cost and savings reconciliation filed with regulators, capital cost savings |  |  |  |  | $ 71,000,000 |  |
Cost and savings reconciliation filed with regulators, operations and maintenance expense |  |  |  |  | $ 18,000,000 |  |
Program costs incurred to date |  |  | $ 1,500,000 |  |  |  |
Advanced Meter System Deployment and Surcharge Request [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Current number of customers that have elected non-standard meter service (in customers) | customer |  |  |  | 104 |  |  |
Advanced Meter System Deployment and Surcharge Request [Member] | Minimum [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Non-standard metering service cost initial fee range |  |  |  |  |  |  | $ 63.97
Advanced Meter System Deployment and Surcharge Request [Member] | Maximum [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Non-standard metering service cost initial fee range |  |  |  |  |  |  | $ 168.61
Transmission Cost of Service Rates [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Requested increase in annual transmission service revenue | $ 4,800,000 |  |  |  |  |  |
Requested rate increase (decrease) | $ 30,200,000 |  |  |  |  |  |

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