The latest date the public utility can issue debt, in CCYY-MM-DD format.

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Electric Capacity

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Minimum monthly bill charge for distributive generation customers.

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Palo Verde Performance Award Period

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Potential refund to customers, pending Final Order

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Amount by which public utilities requested depreciation expense is increased (decreased).

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Show cause order issued by the Federal Energy Regulatory Commission

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Regulation (Narrative) (Details)																						3 Months Ended			9 Months Ended		12 Months Ended
Regulation (Narrative) (Details)	Oct. 25, 2018	Oct. 11, 2018 USD ($)	Jul. 02, 2018 USD ($)	Jun. 28, 2018 USD ($)	May 22, 2018	May 01, 2018 USD ($)	Apr. 01, 2018	Mar. 15, 2018	Mar. 01, 2018 USD ($)	Feb. 15, 2018 USD ($)	Jan. 01, 2018	Dec. 18, 2017 USD ($)	Nov. 01, 2017	Aug. 01, 2017	Jun. 30, 2017 USD ($)	Jun. 29, 2017 USD ($)	Feb. 22, 2017 USD ($)	Jan. 10, 2017	Aug. 25, 2016	Jul. 01, 2016 USD ($)	Jun. 08, 2016 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) MW	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 13, 2018 USD ($)	Apr. 24, 2018 MW	Mar. 20, 2018 MW	Oct. 31, 2017 USD ($)	Oct. 04, 2017 USD ($)	Oct. 07, 2015 USD ($)
Nuclear Decommissioning Funding, Annual Recovery																									$ 74,438,000	$ 80,785,000
Over-collection of fuel revenues, regulatory liability																						$ 9,905,000			$ 9,905,000		$ 6,225,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent																						21.00%	35.00%		21.00%	35.00%	35.00%
NMPRC Case No. 17-00255-UT \| Subsequent Event
Potential refund to customers		$ 1,200,000
Tax benefit refund period		4 months
NMPRC Case No. 18-00016-UT
Public Utilities, Approved Rate Increase (Decrease), Amount						$ (4,900,000)
NMPRC Case No. 18-00116-UT
Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program			$ 400,000
Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program, percentage of expenditures			7.10%
NMPRC Case No. 15-00127-UT
Fuel Reconciliation Period																					24 months
PUCT Docket No. 46831
Recovery of rate case expenses												$ 3,400,000
Surcharge Or Refund Period												3 years
Minimum Distributive Generation Charge												$ 30.00
Nuclear Decommissioning Funding, Annual Recovery												2,100,000
Requested Depreciation Expense, Decrease												$ 1,900,000
Public Utilities, Approved Return on Equity, Percentage												9.65%
PUCT Docket No. 46831 \| Four Corners decommissioning
Decommissioning Costs Increase (Decrease)												$ 5,500,000
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided														7 years
PUCT Docket No. 48124
Public Utilities, Requested Rate Decrease, Amount									$ 22,700,000
Surcharge Or Refund Period							1 year
PUCT Docket No. 46308
Reconcilable Fuel Expense																$ 436,600,000
Fuel Reconciliation Period																36 months
Fuel reconciliation effect, net amount																										$ 5,000,000		$ 5,000,000
Palo Verde Performance Award Period																3 years
PUCT Docket No. 44800 \| Community Solar At Montana Power Station
Electric Capacity \| MW																									3
Number of customers subscribed																						1,500			1,500
Property, Plant and Equipment, Operational Date																									May 31, 2017
PUCT Docket No. 48181 \| Community Solar at Newman
Electric capacity, requested \| MW																															2
NMPRC Case No. 18-00099-UT \| Community Solar at Doña Ana County
Electric capacity, requested \| MW																														2
RGRT \| NMPRC Case No. 15-00280-UT
Debt Instrument, Face Amount																																		$ 65,000,000
Senior Notes \| 4.22% Senior Notes, due 2028
Debt Instrument, Face Amount				$ 125,000,000
Debt Instrument, Issuance Date				Jun. 28, 2018
Debt Instrument, Interest Rate, Stated Percentage				4.22%
Debt Instrument, Maturity Date				Aug. 15, 2028
Senior Notes \| 4.22% Senior Notes, due 2028 \| NMPRC Case No. 17-00217-UT
Debt Instrument, Face Amount				$ 125,000,000
Debt Instrument, Issuance Date				Jun. 28, 2018
Debt Instrument, Interest Rate, Stated Percentage				4.22%
Debt Instrument, Maturity Date				Aug. 15, 2028
Senior Notes \| 4.07% RGRT Senior Notes, due 2025
Debt Instrument, Face Amount				$ 65,000,000
Debt Instrument, Issuance Date				Jun. 28, 2018
Debt Instrument, Interest Rate, Stated Percentage				4.07%
Debt Instrument, Maturity Date				Aug. 15, 2025
Senior Notes \| 4.07% RGRT Senior Notes, due 2025 \| NMPRC Case No. 15-00280-UT
Debt Instrument, Face Amount				$ 65,000,000
Debt Instrument, Issuance Date				Jun. 28, 2018
Debt Instrument, Interest Rate, Stated Percentage				4.07%
Debt Instrument, Maturity Date				Aug. 15, 2025
Non-Fuel Base Rate \| PUCT Docket No. 46831
Public Utilities, Approved Rate Increase (Decrease), Amount												$ 14,500,000
2016 Energy Efficiency Programs \| NMPRC Case No. 13-00176-UT
Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program															$ 400,000
Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program																							$ 400,000
2016 Energy Efficiency Programs \| PUCT Docket No. 47125
Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program										$ 800,000
2017 Energy Efficiency Programs \| NMPRC Case No. 16-00185-UT
Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program																				$ 400,000
Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program																	$ 400,000
2017 Energy Efficiency Programs \| PUCT Docket No. 48332
Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program						$ 1,000,000
Fixed Fuel Factor \| PUCT Docket No. 48264
Increase (Decrease) In Fixed Fuel Factor, Percentage					(29.00%)
Fixed Fuel Factor \| PUCT Docket No. 48781 \| Subsequent Event
Public Utilities, Requested Rate Increase (Decrease), Percentage	(6.99%)
Fixed Fuel Factor \| PUCT Docket No. 46610
Increase (Decrease) In Fixed Fuel Factor, Percentage																		28.80%
Fixed Fuel Factor \| PUCT Docket No. 47692
Increase (Decrease) In Fixed Fuel Factor, Percentage													(19.00%)
2015 Energy Efficiency Programs \| NMPRC Case No. 13-00176-UT
Public Utilities Requested Performance Incentive Bonus Related To Energy Efficiency Program																				$ 300,000
Public Utilities Approved Performance Incentive Bonus Related To Energy Efficiency Program																								$ 300,000
PUCT
Over-collection of fuel revenues, regulatory liability																						$ 6,900,000			$ 6,900,000
Reconcilable Fuel Expense																									$ 335,000,000
Fuel Reconciliation Period																									30 months
Fuel Over And Under Materiality Threshold Percentage																						4.00%			4.00%
PUCT \| Community Solar at Newman
Electric Capacity \| MW																									10
PUCT \| Public Utilities, Regulatory Rate Making Impact
Period To Relate Back New Rates											167 days								80 days
NMPRC
Over-collection of fuel revenues, regulatory liability																						$ 2,900,000			$ 2,900,000
Reconcilable Fuel Expense																									$ 200,100,000
Fuel Reconciliation Period																									45 months
Debt Instrument, Face Amount																													$ 350,000,000				$ 350,000,000
NMPRC \| Holloman
Electric Capacity \| MW																									5
Property, Plant and Equipment, Operational Date																									Oct. 18, 2018
NMPRC \| Public Utilities, Regulatory Rate Making Impact
Public Utilities, Approved Return on Equity, Percentage																					9.48%
NMPRC \| 7.25% 2009 Series B Refunding Bonds, due 2040 \| NMPRC Case No. 17-00217-UT
Debt Instrument, Face Amount																																	$ 37,100,000
Debt Instrument, Interest Rate, Stated Percentage																																	7.25%
NMPRC \| 7.25% 2009 Series A Refunding Bonds, due 2040 \| NMPRC Case No. 17-00217-UT
Debt Instrument, Face Amount																																	$ 63,500,000
Debt Instrument, Interest Rate, Stated Percentage																																	7.25%
NMPRC \| Non-Fuel Base Rate \| Public Utilities, Regulatory Rate Making Impact
Public Utilities, Approved Rate Increase (Decrease), Amount																					$ 600,000
NMPRC \| Utility Cost Of Service \| Public Utilities, Regulatory Rate Making Impact
Public Utilities, Approved Rate Increase (Decrease), Amount																					$ 500,000
FERC
Debt Issuance Authorization Date Range Start																									Nov. 15, 2017
Debt Issuance Authorization Date Range End																									Nov. 14, 2019
Show Cause Orders issued, Number								2
Number of public utilities affected								48
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent																											35.00%
Debt Instrument, Face Amount																													$ 350,000,000			$ 350,000,000
FERC \| Maximum
Period to comply with order from regulatory agency								60 days
FERC \| RGRT
Debt Instrument, Face Amount																																65,000,000
FERC \| 7.25% 2009 Series B Refunding Bonds, due 2040
Debt Instrument, Face Amount																																$ 37,100,000
Debt Instrument, Interest Rate, Stated Percentage																																7.25%
FERC \| 7.25% 2009 Series A Refunding Bonds, due 2040
Debt Instrument, Face Amount																																$ 63,500,000
Debt Instrument, Interest Rate, Stated Percentage																																7.25%
FERC \| Senior Notes \| 4.22% Senior Notes, due 2028
Debt Instrument, Face Amount				$ 125,000,000
Debt Instrument, Issuance Date				Jun. 28, 2018
Debt Instrument, Interest Rate, Stated Percentage				4.22%
Debt Instrument, Maturity Date				Aug. 15, 2028
FERC \| Senior Notes \| 4.07% RGRT Senior Notes, due 2025
Debt Instrument, Face Amount				$ 65,000,000
Debt Instrument, Issuance Date				Jun. 28, 2018
Debt Instrument, Interest Rate, Stated Percentage				4.07%
Debt Instrument, Maturity Date				Aug. 15, 2025