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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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