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Electric Operating Revenues - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) utility	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) utility	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Disaggregation of Revenue [Line Items]
Number of regulated utilities | utility	2		2
Accounts receivable, allowance for credit loss, period increase (decrease)	$ 800,000	$ 400,000	$ 2,400,000	$ 700,000
Contract assets	0		0		$ 0
Texas-New Mexico Power Company
Disaggregation of Revenue [Line Items]
Regulatory assets	1,000,000.0		1,000,000.0
PNM
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 89,200,000		$ 89,200,000		$ 86,200,000

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