Electric Operating Revenues - Narrative (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($) utility	Jun. 30, 2020 USD ($) 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)	$ 400,000	$ 700,000
Contract assets	0	0	$ 0
PNM
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 65,200,000	$ 65,200,000	$ 59,300,000