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Regulatory and Rate Matters - SJGS, Fours Corners and PVNGS Leased Interest Abandonment Applications (Details) $ in Thousands						1 Months Ended
	Apr. 02, 2021 lease MW	Feb. 03, 2021	Jan. 08, 2021 USD ($)	Nov. 01, 2020 USD ($)	Jul. 01, 2019 USD ($)	Nov. 30, 2020 USD ($)	Apr. 14, 2021 MW	Mar. 31, 2021 USD ($) MW	Mar. 12, 2021 MW	Feb. 08, 2021 MW	Jan. 28, 2021 MW	Dec. 31, 2020 USD ($)	Dec. 18, 2020 USD ($)	Nov. 13, 2020 MW	Sep. 28, 2020 USD ($)	Jul. 29, 2020 MW	Mar. 31, 2020 USD ($)	Feb. 21, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
Ownership percentage								50.00%
Regulatory assets								$ 555,150				$ 557,790
Regulatory liabilities								854,748				850,228
Subsequent event
Public Utilities, General Disclosures [Line Items]
Regulatory time frame for proposed PPAs and battery storage agreements	6 months
COVID-19
Public Utilities, General Disclosures [Line Items]
Temporary mandatory moratorium on disconnection period		100 days
Disconnection transition period		90 days
Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW										190
Number of megawatts in battery storage facilities (in megawatts) | MW										100
Solar generation capacity expected to be operational (in megawatts) | MW										50
Facebook Data Center | Subsequent event
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts) | MW							100
PNM
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW																650
Number of megawatts in battery storage facilities (in megawatts) | MW																300
Regulatory assets								456,374				457,953
Regulatory liabilities								663,429				664,873
Solar generation capacity related to unexecuted transmission service agreement (in megawatts) | MW									145
PNM | Four Corners
Public Utilities, General Disclosures [Line Items]
Request issuance of energy transition bonds			$ 300,000
Forecasted undepreciated investment			272,000
Plant decommissioning and coal mine reclamation costs			4,600
Upfront financing costs			7,300
Proceeds from securitization bonds			$ 16,500
Solar generation capacity (in megawatts) | MW											200
Payments for relief from obligations				$ 75,000		$ 15,000
Final payment for relief from obligations						60,000
Initial payment for relief from obligations						$ 15,000
PNM | Four Corners | PNM
Public Utilities, General Disclosures [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners				13.00%
PNM | COVID-19 | COVID-19 Costs Savings
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities								900				900
PNM | Deferred COVID-19 Costs | COVID-19
Public Utilities, General Disclosures [Line Items]
Regulatory assets								$ 10,700				8,800
PNM | Subsequent event
Public Utilities, General Disclosures [Line Items]
Number of leases under which lease term was extended | lease	5
PNM | NMPRC | Subsequent event
Public Utilities, General Disclosures [Line Items]
Solar generation capacity, amount requested for approval to abandon (in megawatts) | MW	114
PNM | Leased Interest Termination on January 15, 2023 | Subsequent event
Public Utilities, General Disclosures [Line Items]
Number of leases under which lease term was extended | lease	4
PNM | Leased Interest Termination on January 15, 2023 | NMPRC | Subsequent event
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW	104
PNM | Leased Interest Termination on January 15, 2024 | NMPRC | Subsequent event
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW	10
PNM | Replacement Resource Portfolio One
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW														200
Number of megawatts in battery storage facilities (in megawatts) | MW														100
PNM | Replacement Resource Portfolio One | Subsequent event
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW	150
Number of megawatts in battery storage facilities (in megawatts) | MW	40
PNM | Replacement Resource Portfolio Two
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW														100
Number of megawatts in battery storage facilities (in megawatts) | MW														30
PNM | Replacement Resource Portfolio Two | Subsequent event
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts) | MW	100
PNM | Replacement Resource Portfolio Three | Subsequent event
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW	300
Number of megawatts in battery storage facilities (in megawatts) | MW	150
PNM | Transportation Electrification Program
Public Utilities, General Disclosures [Line Items]
Expected budgeted expenditures													$ 8,400
Budget flexibility (percent)													25.00%
Budget portion dedicated to low and moderate income customers (percent)													25.00%
PNMR Development
Public Utilities, General Disclosures [Line Items]
Solar generation capacity (in megawatts) | MW								130
Ownership percentage								50.00%
San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Estimated costs of replacement resources															$ 8,100
San Juan Generating Station | Other deferred credits
Public Utilities, General Disclosures [Line Items]
Restructuring reserve												38,100
San Juan Generating Station | Employee Severance
Public Utilities, General Disclosures [Line Items]
Restructuring reserve																	$ 9,400
San Juan Generating Station | PNM
Public Utilities, General Disclosures [Line Items]
Request issuance of energy transition bonds					$ 361,000
Forecasted undepreciated investment					283,000													$ 361,000
Plant decommissioning and coal mine reclamation costs					28,600
Upfront financing costs					9,600
Severance costs					20,000
Proceeds from securitization bonds					$ 19,800
San Juan Generating Station | PNM | Other deferred credits
Public Utilities, General Disclosures [Line Items]
Restructuring reserve												$ 36,800
San Juan Generating Station | PNM | Employee Severance
Public Utilities, General Disclosures [Line Items]
Restructuring reserve																	8,100
San Juan Generating Station | PNM | Other Restructuring
Public Utilities, General Disclosures [Line Items]
Restructuring reserve																	8,900
San Juan Generating Station | PNM | Economic Development and Workforce Training Costs
Public Utilities, General Disclosures [Line Items]
Restructuring reserve																	$ 19,800

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