Electric Operating Revenues - Narrative (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($) utility	Sep. 30, 2020 USD ($) utility	Dec. 31, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Number of regulated utilities \| utility	2	2
Accounts receivable, allowance for credit loss, period increase (decrease)	$ 2,000,000.0	$ 2,700,000
Contract assets	0	0	$ 0
PNM
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 94,400,000	$ 94,400,000	$ 59,300,000

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Amount of increase (decrease) in allowance for credit loss on accounts receivable.

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Carrying amount as of the balance sheet date of the asset arising from commodity contracts such as futures contracts tied to the movement of a particular commodity, which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

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