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Electric Operating Revenue Narrative (Details)	Dec. 31, 2018 USD ($) utility MW	Dec. 31, 2017 USD ($) MW
Contract with Customers, Asset and Liability [Roll Forward]
Number of regulated utilities | utility	2
Contract assets | $	$ 0
Public Service Company of New Mexico
Contract with Customers, Asset and Liability [Roll Forward]
Expected exposure to market risk (in megawatts)	65	65
Power to be sold to third party (in megawatts)	36	36
Public Service Company of New Mexico | Contracts with Customers
Contract with Customers, Asset and Liability [Roll Forward]
Contract with customers, net | $	$ 61,700,000	$ 61,800,000
Palo Verde Nuclear Generating Station Unit 3 | Clean Air Act, SNCR | Public Service Company of New Mexico
Contract with Customers, Asset and Liability [Roll Forward]
Number of megawatts		134

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