Regulatory and Rate Matters - San Juan Generating Station Unit 1 Outage (Details) - San Juan Generating Station $ in Millions	Jun. 30, 2021 USD ($)
San Juan Generating Station Owners \| Insurance Deductible
Public Utilities, Commitments And Contingencies [Line Items]
Estimate of possible loss	$ 2.0
Public Service Company of New Mexico \| Insurance Deductible
Public Utilities, Commitments And Contingencies [Line Items]
Estimate of possible loss	$ 1.0
Public Service Company of New Mexico \| San Juan Generating Station Unit 1
Public Utilities, Commitments And Contingencies [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	50.00%

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
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Balance Type:	debit
Period Type:	instant