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Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) - PNM - Nuclear spent fuel and waste disposal - Palo Verde Nuclear Generating Station - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Public Utilities, Commitments And Contingencies [Line Items]
Estimate of possible loss	$ 59.6
Other deferred credits
Public Utilities, Commitments And Contingencies [Line Items]
Loss contingency accrual	$ 13.0	$ 12.8

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Public Utilities, Commitments And Contingencies [Line Items]

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Amount of loss contingency liability.

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