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Commitments and Contingencies - Nuclear Spent Fuel and Waste Disposal (Details) - Palo Verde Nuclear Generating Station [Member] - Public Service Company of New Mexico [Member] - USD ($)		3 Months Ended
	May. 16, 2014	Mar. 31, 2015	Mar. 31, 2016	Dec. 31, 2015
Department of energy, spent nuclear fuel removal July 2011 - June 2014 [Member]
Public Utilities, Commitments And Contingencies [Line Items]
PNMs share of third party settlement claim		$ 4,300,000
Litigation settlement, portion credited to customers		$ 3,100,000
Nuclear Spent Fuel And Waste Disposal [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Loss contingency, estimate of possible loss			$ 58,000,000
Revised annual fee, nuclear waste disposal	$ 0
Nuclear Spent Fuel And Waste Disposal [Member] \| Other Deferred Credits [Member]
Public Utilities, Commitments And Contingencies [Line Items]
Loss contingency accrual			$ 11,800,000	$ 12,200,000