Regulation	3 Months Ended
Mar. 31, 2017
Public Utilities, General Disclosures [Abstract]
Regulation	Regulation General The rates and services of the Company are regulated by incorporated municipalities in Texas, the PUCT, the NMPRC, and the Federal Energy Regulatory Commission ("FERC"). Municipal orders, ordinances and other agreements regarding rates and services adopted by Texas municipalities are subject to review and approval by the PUCT. The FERC has jurisdiction over the Company's wholesale (sales for resale) transactions, transmission service and compliance with federally-mandated reliability standards. The decisions of the PUCT, the NMPRC and the FERC are subject to judicial review. Texas Regulatory Matters 2015 Texas Retail Rate Case Filing. On August 10, 2015, the Company filed with the City of El Paso, other municipalities incorporated in its Texas service territory, and the PUCT in Docket No. 44941, a request for an annual increase in non-fuel base revenues (the "2015 Texas Retail Rate Case"). On July 21, 2016, the parties to PUCT Docket No. 44941 filed the Joint Motion to Implement Uncontested Amended and Restated Stipulation and Agreement which was unopposed by the parties (the "Unopposed Settlement"). On August 25, 2016, the PUCT approved the Unopposed Settlement and issued its final order in Docket No. 44941 (the "PUCT Final Order"), as proposed. The PUCT Final Order provided for: (i) an annual non-fuel base rate increase, lower annual depreciation expense, a revised return on equity for allowance for funds used during construction ("AFUDC") purposes, and the inclusion of substantially all new plant in service in rate base; (ii) an additional annual non-fuel base rate increase of $3.7 million related to Four Corners Generating Station ("Four Corners") costs, which will be collected through a surcharge terminating on July 12, 2017; (iii) removing the separate rate treatment for residential customers with solar systems that the Company had proposed in its August 10, 2015 filing; (iv) allowing the Company to recover $3.1 million in rate case expenses through a separate surcharge and (v) allowing the Company to recover revenues associated with the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 through a separate surcharge. Interim rates associated with the annual non-fuel base rate increase, became effective on April 1, 2016. The additional surcharges associated with the incremental Four Corners costs, rate case expenses and the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 were implemented on October 1, 2016. For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016. 2017 Texas Retail Rate Case Filing. On February 13, 2017, the Company filed with the City of El Paso, other municipalities incorporated in the Company's Texas service territory and the PUCT in Docket No. 46831, a request for an increase in non-fuel base revenues of approximately $42.5 million. The Company invoked its statutory right to have its new rates relate back for consumption on and after July 18, 2017, which is the 155th day after the filing. The difference in rates that would have been billed will be surcharged or refunded to customers after the PUCT's final order in Docket No. 46831. The PUCT has the authority to require the Company to surcharge or refund such difference over a period not to exceed 18 months. A procedural schedule has been adopted with a hearing scheduled in late August or early September 2017. The Company cannot predict the outcome or the timing of this rate case at this time. Energy Efficiency Cost Recovery Factor. On May 1, 2017, the Company filed its annual application to establish its energy efficiency cost recovery factor for 2018. In addition to projected energy efficiency costs for 2018 and a true-up to prior year actual costs, the Company requested approval of a $1.0 million bonus for the 2016 energy efficiency program results in accordance with PUCT rules. The Company cannot predict the outcome or the timing of this matter at this time. Fuel and Purchased Power Costs. On November 30, 2016, the Company filed a request, which was assigned PUCT Docket No. 46610, to increase its fixed fuel factor by approximately 28.8% to reflect increased fuel expenses primarily related to an increase in the price of natural gas used to generate power. The increase in the fixed fuel factor was effective on an interim basis January 1, 2017 and approved by the PUCT on January 10, 2017. As of March 31, 2017, the Company had under-recovered fuel costs in the amount of $2.5 million for the Texas jurisdiction. Fuel Reconciliation Proceeding. On September 27, 2016, the Company filed an application with the PUCT, designated as PUCT Docket No. 46308, to reconcile $436.6 million of Texas fuel and purchased power expenses incurred during the period of April 1, 2013 through March 31, 2016. On March 31, 2017, the Company requested that the hearing set for April 5, 2017 be postponed until sometime after April 26, 2017 to allow for settlement discussions. The Company and parties to the proceeding have discussed terms of a settlement in principle to resolve the issues in the case, and the Company is currently drafting a stipulation and proposed order for filing with the State Office of Administrative Hearings. The Company expects the PUCT to consider the proposed settlement in the second quarter of 2017. The Company cannot predict the outcome or the timing of this matter. As of March 31, 2017, Texas jurisdictional fuel and purchased power costs subject to a future Texas fuel reconciliation are approximately $140.4 million. Community Solar. On June 8, 2015, the Company filed a petition with the PUCT to initiate a community solar program that includes the construction and ownership of a 3 MW solar photovoltaic system located at Montana Power Station. Participation will be on a voluntary basis, and customers will contract for a set capacity (kW) amount and receive all energy produced. This case was assigned PUCT Docket No. 44800. The Company filed a settlement agreement among all parties on July 1, 2016 approving the program, and the PUCT approved the settlement agreement and program on September 1, 2016. The Community Solar facility is currently under construction and the Company expects completion of the solar facility and commencement of the program in the second quarter of 2017. On April 19, 2017, the Company announced that the entire 3 MW program was fully subscribed by approximately 1,500 Texas customers. Four Corners Generating Station. On February 17, 2015, the Company and Arizona Public Service Company ("APS") entered into an asset purchase agreement (the "Purchase and Sale Agreement") providing for the sale of the Company's interest in Four Corners to APS. The sale of the Company's interest in Four Corners closed on July 6, 2016. On June 10, 2015, the Company filed an application in Texas requesting reasonableness and public interest findings and certain rate and accounting findings related to the Purchase and Sale Agreement. This case was assigned PUCT Docket No. 44805. Subsequent to the filing of the application, the case has been subject to numerous procedural matters, including a March 23, 2016 order in which the PUCT determined not to dismiss the reasonableness and public interest issues in this docket but to consider the requested rate and accounting findings, including coal mine reclamation costs, in a rate case proceeding. On September 1, 2016, a motion by parties in the proceeding to suspend the procedural schedule in order to pursue settlement was approved. On March 3, 2017, the Company filed a Joint Motion to Implement Stipulation and Agreement, and commission Staff filed its recommendation that the Company’s disposition of its interest in Four Corners was reasonable and consistent with the public interest. A final order approving the Stipulation and Agreement was adopted by the PUCT on March 30, 2017. At March 31, 2017, the regulatory asset associated with the Four Corners coal mine reclamation costs for the Company's Texas jurisdiction was approximately $7.1 million. Until otherwise determined, the Company will continue to recover its coal mine reclamation costs in Texas under previous orders and decisions of the PUCT. The Stipulation and Agreement also acknowledged an agreement among the parties related to the rate and accounting treatment of certain costs of Four Corners, including coal mine reclamation costs. Pursuant to the PUCT's order in PUCT Docket No. 44805, recovery of these costs will be addressed in future base rate and fuel-related proceedings. If the PUCT makes a determination that results in changes to how existing regulatory assets or previously incurred costs for Four Corners are recovered in rates, any such changes will be recognized for financial reporting purposes only when it becomes probable future cash flows will change as a result of such regulatory actions. Other Required Approvals. The Company has obtained other required approvals for tariffs and approvals required by the Public Utility Regulatory Act (the "PURA") and the PUCT. New Mexico Regulatory Matters 2015 New Mexico Rate Case Filing. On May 11, 2015, the Company filed a request with the NMPRC, in Case No. 15-00127-UT, for an annual increase in non-fuel base rates. On June 8, 2016, the NMPRC issued its final order in Case No. 15-00127-UT (the "NMPRC Final Order"), which approved an annual increase in non-fuel base rates of approximately $0.6 million, an increase of approximately $0.5 million in other service fees and a decrease in the Company's allowed return on equity to 9.48%. The NMPRC Final Order concluded that all of the Company's new plant in service was reasonable and necessary and therefore would be recoverable in rates. The Company's rates were approved by the NMPRC effective July 1, 2016 and implemented at such time. 2017 New Mexico Rate Case Filing. NMPRC Case No. 15-00109-UT required the Company to make a rate filing in New Mexico in the second quarter of 2017 using a historical test year ended December 31, 2016. On March 24, 2017, the Company, NMPRC Utility Division Staff and the New Mexico Attorney General filed a Joint Motion to Modify Filing Date Stated in Final Order requesting that the rate filing date be changed to no later than July 31, 2019, using the appropriate historical test year period. The joint request was approved by the NMPRC on April 12, 2017. Fuel and Purchased Power Costs. Historically, fuel and purchased power costs were recovered through base rates and a Fuel and Purchased Power Cost Adjustment Clause ("FPPCAC") that accounts for changes in the costs of fuel relative to the amount included in base rates. Effective July 1, 2016, with the implementation of the final order in Case No. 15-00127-UT, fuel and purchased power costs are no longer recovered through base rates but are recovered through the FPPCAC. The Company's request to reconcile its fuel and purchased power costs for the period January 1, 2013 through December 31, 2014 was approved in Case No. 15-00127-UT. New Mexico jurisdictional costs subject to prudence review are costs from January 1, 2015 through March 31, 2017 that total approximately $127.5 million. At March 31, 2017, the Company had a net fuel over-recovery balance of approximately $0.2 million in New Mexico. 5 MW Holloman Air Force Base ("HAFB") Facility CCN. On October 7, 2015, in NMPRC Case No. 15-00185-UT, the NMPRC issued a final order approving a CCN for a 5 MW solar power generation facility located on HAFB in the Company's service territory in New Mexico. The Company and HAFB negotiated a special retail contract, which includes power sales agreement for the facility, to replace the existing load retention agreement which was approved by final order issued October 5, 2016 in NMPRC Case No. 16-00224-UT. Construction of the solar generation facility is expected to be completed in the fourth quarter of 2017 or early 2018. New Mexico Efficient Use of Energy Recovery Factor. On July 1, 2016, the Company filed its annual application requesting approval of its 2017 Energy Efficiency and Load Management Plan and to establish energy efficiency cost recovery factors for 2017. In addition to projected energy efficiency costs for 2017, the Company requested approval of a $0.4 million incentive for 2017 energy efficiency programs in accordance with NMPRC rules. This case was assigned Case No. 16-00185-UT. On February 22, 2017, the NMPRC issued a Final Order approving the Company’s 2017 Energy Efficiency and Load Management Plan and authorizing recovery in 2017 of a base incentive of $0.4 million. The Company’s energy efficiency cost recovery factors were approved and effective in customer bills beginning on March 1, 2017. In addition, on July 1, 2016, the Company filed its 2015 Annual Report for Energy Efficiency Programs, which included an incentive for verified 2015 program performance of $0.3 million, which was approved in Case No. 13-00176-UT. The Company recorded the $0.3 million approved incentive in operating revenues in the first quarter of 2017. Other Required Approvals. The Company has obtained other required approvals for other tariffs, securities transactions, recovery of energy efficiency costs through a base rate rider and other approvals as required by the NMPRC. Federal Regulatory Matters The Company has obtained required approvals for rates and tariffs, securities transactions and other approvals as required by the FERC.

Regulation

General

The rates and services of the Company are regulated by incorporated municipalities in Texas, the PUCT, the NMPRC, and the Federal Energy Regulatory Commission ("FERC"). Municipal orders, ordinances and other agreements regarding rates and services adopted by Texas municipalities are subject to review and approval by the PUCT. The FERC has jurisdiction over the Company's wholesale (sales for resale) transactions, transmission service and compliance with federally-mandated reliability standards. The decisions of the PUCT, the NMPRC and the FERC are subject to judicial review.

Texas Regulatory Matters

2015 Texas Retail Rate Case Filing. On August 10, 2015, the Company filed with the City of El Paso, other municipalities incorporated in its Texas service territory, and the PUCT in Docket No. 44941, a request for an annual increase in non-fuel base revenues (the "2015 Texas Retail Rate Case").

On July 21, 2016, the parties to PUCT Docket No. 44941 filed the Joint Motion to Implement Uncontested Amended and Restated Stipulation and Agreement which was unopposed by the parties (the "Unopposed Settlement"). On August 25, 2016, the PUCT approved the Unopposed Settlement and issued its final order in Docket No. 44941 (the "PUCT Final Order"), as proposed. The PUCT Final Order provided for: (i) an annual non-fuel base rate increase, lower annual depreciation expense, a revised return on equity for allowance for funds used during construction ("AFUDC") purposes, and the inclusion of substantially all new plant in service in rate base; (ii) an additional annual non-fuel base rate increase of $3.7 million related to Four Corners Generating Station ("Four Corners") costs, which will be collected through a surcharge terminating on July 12, 2017; (iii) removing the separate rate treatment for residential customers with solar systems that the Company had proposed in its August 10, 2015 filing; (iv) allowing the Company to recover $3.1 million in rate case expenses through a separate surcharge and (v) allowing the Company to recover revenues associated with the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 through a separate surcharge.

Interim rates associated with the annual non-fuel base rate increase, became effective on April 1, 2016. The additional surcharges associated with the incremental Four Corners costs, rate case expenses and the relate back of rates to consumption on and after January 12, 2016 through March 31, 2016 were implemented on October 1, 2016.

For financial reporting purposes, the Company deferred any recognition of the Company's request in its 2015 Texas Retail Rate Case until it received the PUCT Final Order on August 25, 2016. Accordingly, it reported in the third quarter of 2016 the cumulative effect of the PUCT Final Order which related back to January 12, 2016.

2017 Texas Retail Rate Case Filing. On February 13, 2017, the Company filed with the City of El Paso, other municipalities incorporated in the Company's Texas service territory and the PUCT in Docket No. 46831, a request for an increase in non-fuel base revenues of approximately $42.5 million. The Company invoked its statutory right to have its new rates relate back for consumption on and after July 18, 2017, which is the 155th day after the filing. The difference in rates that would have been billed will be surcharged or refunded to customers after the PUCT's final order in Docket No. 46831. The PUCT has the authority to require the Company to surcharge or refund such difference over a period not to exceed 18 months. A procedural schedule has been adopted with a hearing scheduled in late August or early September 2017. The Company cannot predict the outcome or the timing of this rate case at this time.

Energy Efficiency Cost Recovery Factor. On May 1, 2017, the Company filed its annual application to establish its energy efficiency cost recovery factor for 2018. In addition to projected energy efficiency costs for 2018 and a true-up to prior year actual costs, the Company requested approval of a $1.0 million bonus for the 2016 energy efficiency program results in accordance with PUCT rules. The Company cannot predict the outcome or the timing of this matter at this time.

Fuel and Purchased Power Costs. On November 30, 2016, the Company filed a request, which was assigned PUCT Docket No. 46610, to increase its fixed fuel factor by approximately 28.8% to reflect increased fuel expenses primarily related to an increase in the price of natural gas used to generate power. The increase in the fixed fuel factor was effective on an interim basis January 1, 2017 and approved by the PUCT on January 10, 2017. As of March 31, 2017, the Company had under-recovered fuel costs in the amount of $2.5 million for the Texas jurisdiction.

Fuel Reconciliation Proceeding. On September 27, 2016, the Company filed an application with the PUCT, designated as PUCT Docket No. 46308, to reconcile $436.6 million of Texas fuel and purchased power expenses incurred during the period of April 1, 2013 through March 31, 2016. On March 31, 2017, the Company requested that the hearing set for April 5, 2017 be postponed until sometime after April 26, 2017 to allow for settlement discussions. The Company and parties to the proceeding have discussed terms of a settlement in principle to resolve the issues in the case, and the Company is currently drafting a stipulation and proposed order for filing with the State Office of Administrative Hearings. The Company expects the PUCT to consider the proposed settlement in the second quarter of 2017. The Company cannot predict the outcome or the timing of this matter. As of March 31, 2017, Texas jurisdictional fuel and purchased power costs subject to a future Texas fuel reconciliation are approximately $140.4 million.

Community Solar. On June 8, 2015, the Company filed a petition with the PUCT to initiate a community solar program that includes the construction and ownership of a 3 MW solar photovoltaic system located at Montana Power Station. Participation will be on a voluntary basis, and customers will contract for a set capacity (kW) amount and receive all energy produced. This case was assigned PUCT Docket No. 44800. The Company filed a settlement agreement among all parties on July 1, 2016 approving the program, and the PUCT approved the settlement agreement and program on September 1, 2016. The Community Solar facility is currently under construction and the Company expects completion of the solar facility and commencement of the program in the second quarter of 2017. On April 19, 2017, the Company announced that the entire 3 MW program was fully subscribed by approximately 1,500 Texas customers.

Four Corners Generating Station. On February 17, 2015, the Company and Arizona Public Service Company ("APS") entered into an asset purchase agreement (the "Purchase and Sale Agreement") providing for the sale of the Company's interest in Four Corners to APS. The sale of the Company's interest in Four Corners closed on July 6, 2016.

On June 10, 2015, the Company filed an application in Texas requesting reasonableness and public interest findings and certain rate and accounting findings related to the Purchase and Sale Agreement. This case was assigned PUCT Docket No. 44805. Subsequent to the filing of the application, the case has been subject to numerous procedural matters, including a March 23, 2016 order in which the PUCT determined not to dismiss the reasonableness and public interest issues in this docket but to consider the requested rate and accounting findings, including coal mine reclamation costs, in a rate case proceeding. On September 1, 2016, a motion by parties in the proceeding to suspend the procedural schedule in order to pursue settlement was approved. On March 3, 2017, the Company filed a Joint Motion to Implement Stipulation and Agreement, and commission Staff filed its recommendation that the Company’s disposition of its interest in Four Corners was reasonable and consistent with the public interest. A final order approving the Stipulation and Agreement was adopted by the PUCT on March 30, 2017.

At March 31, 2017, the regulatory asset associated with the Four Corners coal mine reclamation costs for the Company's Texas jurisdiction was approximately $7.1 million. Until otherwise determined, the Company will continue to recover its coal mine reclamation costs in Texas under previous orders and decisions of the PUCT. The Stipulation and Agreement also acknowledged an agreement among the parties related to the rate and accounting treatment of certain costs of Four Corners, including coal mine reclamation costs. Pursuant to the PUCT's order in PUCT Docket No. 44805, recovery of these costs will be addressed in future base rate and fuel-related proceedings. If the PUCT makes a determination that results in changes to how existing regulatory assets or previously incurred costs for Four Corners are recovered in rates, any such changes will be recognized for financial reporting purposes only when it becomes probable future cash flows will change as a result of such regulatory actions.

Other Required Approvals. The Company has obtained other required approvals for tariffs and approvals required by the Public Utility Regulatory Act (the "PURA") and the PUCT.

New Mexico Regulatory Matters

2015 New Mexico Rate Case Filing. On May 11, 2015, the Company filed a request with the NMPRC, in Case No. 15-00127-UT, for an annual increase in non-fuel base rates. On June 8, 2016, the NMPRC issued its final order in Case No. 15-00127-UT (the "NMPRC Final Order"), which approved an annual increase in non-fuel base rates of approximately $0.6 million, an increase of approximately $0.5 million in other service fees and a decrease in the Company's allowed return on equity to 9.48%. The NMPRC Final Order concluded that all of the Company's new plant in service was reasonable and necessary and therefore would be recoverable in rates. The Company's rates were approved by the NMPRC effective July 1, 2016 and implemented at such time.

2017 New Mexico Rate Case Filing. NMPRC Case No. 15-00109-UT required the Company to make a rate filing in New Mexico in the second quarter of 2017 using a historical test year ended December 31, 2016. On March 24, 2017, the Company, NMPRC Utility Division Staff and the New Mexico Attorney General filed a Joint Motion to Modify Filing Date Stated in Final Order requesting that the rate filing date be changed to no later than July 31, 2019, using the appropriate historical test year period. The joint request was approved by the NMPRC on April 12, 2017.

Fuel and Purchased Power Costs. Historically, fuel and purchased power costs were recovered through base rates and a Fuel and Purchased Power Cost Adjustment Clause ("FPPCAC") that accounts for changes in the costs of fuel relative to the amount included in base rates. Effective July 1, 2016, with the implementation of the final order in Case No. 15-00127-UT, fuel and purchased power costs are no longer recovered through base rates but are recovered through the FPPCAC. The Company's request to reconcile its fuel and purchased power costs for the period January 1, 2013 through December 31, 2014 was approved in Case No. 15-00127-UT. New Mexico jurisdictional costs subject to prudence review are costs from January 1, 2015 through March 31, 2017 that total approximately $127.5 million. At March 31, 2017, the Company had a net fuel over-recovery balance of approximately $0.2 million in New Mexico.

5 MW Holloman Air Force Base ("HAFB") Facility CCN. On October 7, 2015, in NMPRC Case No. 15-00185-UT, the NMPRC issued a final order approving a CCN for a 5 MW solar power generation facility located on HAFB in the Company's service territory in New Mexico. The Company and HAFB negotiated a special retail contract, which includes power sales agreement for the facility, to replace the existing load retention agreement which was approved by final order issued October 5, 2016 in NMPRC Case No. 16-00224-UT. Construction of the solar generation facility is expected to be completed in the fourth quarter of 2017 or early 2018.

New Mexico Efficient Use of Energy Recovery Factor. On July 1, 2016, the Company filed its annual application requesting approval of its 2017 Energy Efficiency and Load Management Plan and to establish energy efficiency cost recovery factors for 2017. In addition to projected energy efficiency costs for 2017, the Company requested approval of a $0.4 million incentive for 2017 energy efficiency programs in accordance with NMPRC rules. This case was assigned Case No. 16-00185-UT. On February 22, 2017, the NMPRC issued a Final Order approving the Company’s 2017 Energy Efficiency and Load Management Plan and authorizing recovery in 2017 of a base incentive of $0.4 million. The Company’s energy efficiency cost recovery factors were approved and effective in customer bills beginning on March 1, 2017. In addition, on July 1, 2016, the Company filed its 2015 Annual Report for Energy Efficiency Programs, which included an incentive for verified 2015 program performance of $0.3 million, which was approved in Case No. 13-00176-UT. The Company recorded the $0.3 million approved incentive in operating revenues in the first quarter of 2017.

Other Required Approvals. The Company has obtained other required approvals for other tariffs, securities transactions, recovery of energy efficiency costs through a base rate rider and other approvals as required by the NMPRC.

Federal Regulatory Matters

The Company has obtained required approvals for rates and tariffs, securities transactions and other approvals as required by the FERC.