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Regulatory and Rate Matters - TNMP Narrative (Details) advanced_meter in Thousands, $ in Thousands									1 Months Ended			3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 26, 2022 USD ($)	Jul. 01, 2021 USD ($)	Apr. 05, 2021 USD ($)	Jun. 26, 2020 USD ($)	Apr. 06, 2020 USD ($)	Dec. 20, 2018 USD ($)	May 30, 2018 USD ($)	Jan. 10, 2018 USD ($)	Oct. 31, 2019 USD ($)	Aug. 31, 2019 USD ($)	Jul. 31, 2011 USD ($)	Mar. 31, 2021	Dec. 31, 2018 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) advanced_meter	Dec. 31, 2021 USD ($)	Jul. 28, 2021 USD ($)	May 27, 2021 USD ($)	Dec. 31, 2020 USD ($)	Oct. 02, 2020 USD ($)	Dec. 31, 2019 USD ($)
Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities																	$ 662,146			$ 670,292
Texas-New Mexico Power Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities																	$ 187,563			$ 187,407
Refund of regulatory liability to customers															$ 37,800
Estimate of possible upgrades																					$ 46,000
Energy efficiency cost recovery factor, requested change amount																			$ 7,200
Energy efficiency cost recovery factor, requested performance bonus																		$ 2,300	$ 2,300
Requested increase annual distribution revenue requirement		$ 13,500	$ 14,000		$ 14,700
Incremental distribution investments			$ 104,500		$ 149,200
Annual distribution revenue requirement				$ 14,300
Texas-New Mexico Power Company | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested increase annual distribution revenue requirement	$ 14,200
Incremental distribution investments	$ 95,600
Texas-New Mexico Power Company | 2018 TNMP Rate Case
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)						$ 10,000	$ 25,900
Requested return on equity						9.65%	10.50%
Requested cost of debt, percentage							7.20%
Requested debt capital structure, percentage						55.00%	50.00%
Requested equity capital structure, percentage						45.00%	50.00%
Refund of federal income tax rates period														3 years
Investments excluded from rate, amount						$ 10,600
Recovery of direct costs									$ 3,300	$ 3,800
Remaining recovery period of regulatory assets for which no return investment during recovery period is provided									3 years	3 years
Write off regulatory disallowance																						$ 500
Texas-New Mexico Power Company | Advanced Meter System Deployment and Surcharge Request
Public Utilities, General Disclosures [Line Items]
Approved deployment costs											$ 113,400
Period of time to collect deployment costs through surcharge period											12 years
Number of advanced meters installed | advanced_meter																242
NMPRC
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)																$ 99,200
Requested return on equity																10.125%
Proposed term for providing benefits to customers related to reduction in state corporate tax												3 years			23 years
NMPRC | Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)								$ 10,300
Requested return on equity								9.575%
Proposed term for providing benefits to customers related to reduction in state corporate tax								3 years
PUCT | Texas-New Mexico Power Company
Public Utilities, General Disclosures [Line Items]
Costs of deployment													$ 9,000

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