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Regulatory and Rate Matters - SJGS Abandonment Application (Details) $ in Millions			12 Months Ended
	Apr. 01, 2020 USD ($)	Jul. 01, 2019 USD ($) scenario MW	Dec. 31, 2020 USD ($)	Nov. 13, 2020 MW	Sep. 28, 2020 USD ($) MW	Jun. 30, 2020 USD ($)	Jun. 24, 2020 MW	Mar. 27, 2020 MMBTU MW	Feb. 21, 2020 USD ($)	May 31, 2019 MW
PNM Solar Direct
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)										50
Replacement Resource Portfolio Two | Hearing Examiners Approach Two
Public Utilities, General Disclosures [Line Items]
Number of megawatts for natural gas facility (in Megawatts)							200
Replacement Resource Portfolio Four | Hearing Examiners Approach One
Public Utilities, General Disclosures [Line Items]
Number of megawatts for demand response (in Megawatts)							24
Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)								40
Solar distributed generation (in mw)								300
Solar generation capacity, power purchase agreements (in Megawatts) | MMBTU								20
Public Service Company of New Mexico | PNM Solar Direct
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)								50
Public Service Company of New Mexico | Replacement Resource Portfolio One | Hearing Examiners Approach One
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)							150
Solar distributed generation (in mw)							300
Public Service Company of New Mexico | Replacement Resource Portfolio Two | Hearing Examiners Approach One
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)							20
Solar distributed generation (in mw)							50
Public Service Company of New Mexico | Replacement Resource Portfolio Three
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)				100	100
Solar distributed generation (in mw)				200	200
Public Service Company of New Mexico | Replacement Resource Portfolio Three | Hearing Examiners Approach One
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)							100
Solar distributed generation (in mw)							200
Public Service Company of New Mexico | Replacement Resource Portfolio Four
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)				30	30
Solar distributed generation (in mw)				100	100
Public Service Company of New Mexico | Replacement Resource Portfolio Four | Hearing Examiners Approach One
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)							30
Solar distributed generation (in mw)							100
Public Service Company of New Mexico | Replacement Resource Portfolio Five
Public Utilities, General Disclosures [Line Items]
Number of megawatts in battery storage facilities (in megawatts)				130	130
Solar distributed generation (in mw)				299	299
San Juan Generating Station
Public Utilities, General Disclosures [Line Items]
Estimated costs of replacement resources | $					$ 8.1
San Juan Generating Station | Other deferred credits
Public Utilities, General Disclosures [Line Items]
Restructuring reserve | $			$ 38.1
San Juan Generating Station | Employee Severance
Public Utilities, General Disclosures [Line Items]
Restructuring reserve | $						$ 9.4
San Juan Generating Station | Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Number of megawatts in natural gas-fired peaking plant (in megawatts)		280
Number of megawatts in battery storage facilities (in megawatts)		70
Solar distributed generation (in mw)		350
Number of megawatts in battery storage facilities, replacement resource scenario (in megawatts)		60
Number of replacement resource scenarios | scenario		3
Request issuance of energy transition bonds | $	$ 361.0	$ 361.0
Forecasted undepreciated investment | $			283.0						$ 361.0
Plant decommissioning and coal mine reclamation costs | $			28.6
Upfront financing costs | $			9.6
Severance costs | $			20.0
Proceeds from securitization bonds | $		$ 19.8
San Juan Generating Station | Public Service Company of New Mexico | Other deferred credits
Public Utilities, General Disclosures [Line Items]
Restructuring reserve | $			$ 36.8
San Juan Generating Station | Public Service Company of New Mexico | Employee Severance
Public Utilities, General Disclosures [Line Items]
Restructuring reserve | $						8.1
San Juan Generating Station | Public Service Company of New Mexico | Other Restructuring
Public Utilities, General Disclosures [Line Items]
Restructuring reserve | $						8.9
San Juan Generating Station | Public Service Company of New Mexico | Economic Development and Workforce Training Costs
Public Utilities, General Disclosures [Line Items]
Restructuring reserve | $						$ 19.8

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